The biggest issue with bounce lands is that you have to take off your turn two to play them. At least with gain lands you can play them on turn 1, which is a less valuable turn for most decks.
First off Isochron Scepter is definitely not unbeatable, and neither is Sylvan Library. I can understand not including them, but it wouldn't be because they are too strong.
I am also not a big fan of having a lifegain theme in cube, because I think it just hoses aggressive strategies too hard. It's so hard to finish your oppponent off fast if they play three or four lifegain spells in a single game, and also the payoffs for lifegain just aren't really good enough in my opinion without playing multiples of cards like ajani's pridemate.
WHITE - Add more aggressive creatures and cut some medium power level spells.
BLACK - I personally would recommend trying to get more aggressive in this color, but I'll admit that's probably my own bias and love of cards like Carnophage. I'd also agree with you that Buried Alive probably isn't good enough. Reanimation strategies, even in the most powerful of peasant lists, just aren't that great. Even if you just throw in another 1B removal spell, you'll probably be better off there.
RED - Again, here I think your aggro could use some help. You have a lot of four drops, and not very many one or two drops. Red is notorious for being the most aggressive color, so this is probably the most important update I can recommend. Other than that, I think your selection of burn spells could be upgraded a little, but for the most part looks pretty good. If anything there, I'd recommend trying to move away from stuff like Inescapable Flames in favor of cards like Rolling Earthquake or Slice and Dice to give red more of a role in control decks.
MULTI - Overall I would decrease the size of this section. Less gold cards is a good thing for your drafters is a good thing, especially given your restrictions on cards that are accessible to you. I would look to get this down to three per guild, or at least four per guild. Try to run gold cards that guide your drafters toward the archetypes you want to support in those color pairs. In Azorius, for example, I would probably cut the charm since it's less generically powerful than the Reflector Mage and doesn't necessarily support a UW Flyers deck the same way that Cloudblazer and Skyknight do.
COLORLESS - Here I'd say you need more mana rocks, though I understand how those may not be accessible. I'd be looking for generic rocks, signets, talismen, etc. Any two casting cost mana rocks you can get your hands one would overall improve this section. I might also shy away from cards like Loxodon Warhammer in a cube that tends to be over all lower in power level. Warhammer can be a very powerful, often game winning card. Personally I run it and love it, but I'm also running Skullclamp and the like.
LANDS - I prefer the gain lands to the Karoos that you're currently running if you want a full cycle. If that's a card access limitation, the Karoos are perfectly ok fixers.
Hopefully this is helpful. I also run a 360 peasant list if you want to check it out. The link is in my signature. Thanks for posting! More peasant cubers is never a bad thing. Grin