High frequency bots don't have high influence/rshares. It's a trade off. You either have high frequency (voting on more posts), or high influence/rshares on less posts, but not both. There is only 20% VP regenerated everyday.

Since everyone can create accounts for free (registration fee is deposited into new account), number of accounts is not actually a barrier for bot runners -- they're already scripting everything. Sure it will need some work/efforts, but it won't stop them.

//Edit: forgot this: in current code, there is a penalty when calculating VP regeneration. The penalty is larger for voters with higher frequency.