First 2 points crap. Third one good
Heh, there already was a huge wealth of persistent rumours about some people buying votes and whatnot. I guess everybody using multiple accounts to vote for themselves is a given. Underneath that, there is the whole metagame about some popularity contest going; Who has most friends, biggest guild. Who works hardest to shill his own castle on forums, chat etc. You can easily make some sort of " yeah?! all part of the game!!" argument about most of this stuff. However, it is undeniable all of it is very detrimental to the base setting. ie, people voting for a design they like best and this most liked design then becoming available.
Now, if on top of all that you add a huge, significant reward for winning the contest...I assume the sleaze and corruption and bribery to ensure """I WIN!!!" would defy all description. It'd contribute towards ensuring stuff chosen are always anything but community favorites.
Situation where devs make it incredibly clear community won't pick anything and voting means nothing except helps underlining some of the most interesting plots for devs to look at .. That'd be a situation that could afford some epic rewards. Just that I'm not sure if I like that alternative better than current situation where votes genuinely counted in a moderately stake-free setting.
Just..give..us..the..damn..design..tool. Assuming tech and code truly allows it, tis ridiculous they refuse to let people design their own keeps and castles.