The idea of XP upgrade would let players who do well in games (Above average place and more importantly for xp, conquer a lot of tiles) would get an extra percent so that if they play good for a long time, they can reach the top faster. If the players are below average and can hardly win a game (I'm not mocking, it's just how it is), then the 5%, 10% would not make much of a difference either way due to the low xp winning. Also, that way, the so called "grinders" (People who play as many games as possible in as little time as possible) would not get these bonuses and would fall behind in both the XP rank and Strength rank. If anyone is to say that the weaker one's should have more motivation experience wise, I believe this is not the case. It would be more useful if we could see the whole XP rank list, not just the TOP 10 and yourself (actually just the statistics not the actual position.Also if you aren't in the TOP 10, you can't know how much you need to rise in the leader board.) Lastly on this idea, how many below average players are shooting for the Level 39 or 2047Matches or 912 Wins and these numbers do not stop rising

About the friend/foe list, I'm sorry that I haven't made myself clear, but I believe I saw a post about it's benefits and ideas. Anyway, I just looked at it like this: as you form friends with who you play constantly, thus saving time on waiters/quiters and obnoxious people. Yes it would take some time to form such people, but after a while, it would be just really interconnected (Friends bring other friends and so on). The foe list is basically like a ban list, people who can't join your game, or if you see them in other games lets say the system informs you in some way. That would prevent a lot of unpleasant situations and after a while, I guess the list could become quite big. All this points to the ranking in systems stability. The reason behind this is that once huge webs of friends and foes form, the game could sustain more reasonable plays with realistic situations (I assume friends don't surrender prematurely or get kicked because of idle turns), therefore more games would be complete and thus the actual points gained or lost would be closer to reality.
I hope I made my points clear, if something still seems off, please point to it and I will try to put it in as little number of sentences with as much meaning to them as possible