The bad thing of capping that it can start discussion like: "you can't do anything unless you pay" and those new players will be pretty hard to convince that 50 stats are pretty good to do really alot... They will still say "you can't do anything" and as there is no other marketing except word to mouth - it can have great influence. However, I have no reasonable ideas on other ways of monetezation that'd be new and not mentioned in this topic already...
Also, please overcome your vision on sending e-mails and notify your playerbase about start of a new world. It is perfectly OK.