I like your question.
I once created a campaign in which every level of a dungeon was associated with both one of the Seven Deadly Sins and one of the Seven Virtues.
But also, following up on your question, I think any number of virtuous traits counter-act envy. Now admittedly envy has never been a vice from which I have suffered. It isn't in my personality, anger has throughout most of my life been my chief defect of soul and nature.
Nevertheless I once developed a set of prayers based on the Vices and Virtues.
Lord, help me to overcome the Deadly Sins.
Belittle and humble my pride, destroy any envy I have ever felt for anyone, grant me self control over any gluttony and lack of discipline I may ever be tempted to indulge, control my lust and reduce it to moderation and righteous pleasure, tame my anger, my greatest fault, and instead instill patience and gentleness, dispose forever of my despair and lack of faith, kill my greed and replace it with generosity, obliterate sloth and procrastination within myself and instead fire me to be of service to others and at beneficial work.
Lord, help me to promote and instill within myself the Great Virtues of Righteousness
Lord make me Chaste, Vigilant, and Courageous, make me Abstinent, Prudent, Temperate, and Moderate, create within me a spirit of Liberality, Charity, and Generosity, make me Diligent and Zealous of what is good and needful, help me to become ever more Patient, Merciful, and Forbearing with the innocent and the reforming, and Just and Honest with the selfish and dishonest, give me much Faith and Great Hope, help me to be Kind and Peaceful, even towards my enemies, grant me Fortitude, Strength that does not falter, and Endurance that does not tire, and make me Wise, Free of Fear and Equitable in all things, and ever more like Yourself in everything. Above all else plant Love in my Heart and success in my Actions.
Given that, and based personally on my own experience and what I've observed of others, I'd say that a number of traits serve to counteract Envy. Courage, Vigilance, Abstinence (I'm not speaking necessarily of sexual abstinence of chastity, but if you can learn to patiently become abstinent, then regardless of whether you have a lot or a little, it doesn't matter at all to you what others have), Liberality (not used as a political term, but as a trait of temperament), Peacefulness, Patience, Equanimity, and Hope. I also liked your list, especially Gratitude (an often well-overlooked virtue in the modern world, I'm afraid). I also wouldn't overlook Joy. You can be both joyously happy with your own situation and joyously glad of the success of others. And because of that you wish them success. Joy is a good trait.
Of course Love is the big one I suspect. It's hard to envy anyone you truly love.
By the by, I also personally think one of the real virtues that is often overlooked though is humor.
Good Humor kills a myriad of Vices.
Like envy for instance. It also teaches you not to take yourself so seriously, not to take others so seriously, and it's really good as an antidote to anger. Very effective.
Anywho I don't know if that's what you're looking for, but it's what struck me about your questions.
From a gaming standpoint, I would say the opposite of envy is "acceptance of other people's good fortune"
I say this because it is more interactive with the environment/NPCs.
Compared to your other option which is more self reflective and you can't as easily build a story out of self reflection, that is something completely player-motivated, where as with environment-interaction, as the DM you have more input in to allowing more scenarios/opportunities for such a thing to happen.
That's a good general point. I'd say from a gaming and storytelling standpoint you want to tie both virtues and vices more or less directly to actions, behaviors, and situations. Or put another way, virtues and vices are virtues and vices because of what they do, rather than just symbolize.
P.S.: By the way, I wanted to add a little something just as an observation and bit of speculation. I personally think all of the Vices have their corresponding positive or beneficial expression. Not an opposite, so much as a beneficial expression of themselves.
For instance with Envy, I think there is a very beneficial kind of Envy. That is a sort of "spiritual, or even psychological (as the Greeks meant it - of the soul) envy." A envy that encourages virtue. For instance one can very much envy the admirable qualities of another person, to the degree that one envies the positive and beneficial qualities apparent in the other person so much that one is encouraged to emulate those same qualities. For example you can envy the beneficial success of another and then set out to emulate it. If you do so in a positive and beneficial way yourself then the vice of Envy had actually become the Virtue of Envy.
The same might be said of hatred. One might hate injustice. So much so that one sets out to correct injustice, and to promote Justice. (And after all what good does it do to hate injustice unless you're willing to do something about it? Otherwise you don't really hate injustice, you're just mildly annoyed or inconvenienced by it.) In a case like that the vice of hatred has become the Virtue of Hatred.
And of course the opposite might be said of the Virtues. Each virtue can have a negative expression. For sentence you might be chaste yourself, to control and discipline your own behavior, but then that leads you to attempt to forcefully or tyrannically impose a sort of artificial chastity on all others.
Or take Vigilance, which is ordinarily a very useful and beneficial Virtue, can through misapplication become a disturbing, suspicious, and even unjust method of behavior. It depends on the circumstances and the degree to which one is willing to set boundaries as to whether a Virtue remains a virtue, or transforms into a vice, and it depends upon one's motivation coupled with one's actual behavior as to whether a vice will cripple a man or transmute into a potentially useful Virtue.
I only mention this because in storytelling, and in life, such reverse applications often make for far more interesting examinations of Virtues and Vices than do the obvious and straightforward ones of compare and contrast.
A vice that becomes a virtue, and/or a virtue obscured, are of course stories as old as man.
Well, I'm gonna hit the bunk.
