Just bought one! Can I buy two? ... Alas, I can't!
But I totally would, and I'm sure several others would too!
Just my two cents, or rather my $25, I think you should have different Supporter Tiers, and leave it uncapped.
Like, for $5, you get one month ad-free, $10 three months, $25 forever...
$50 or more = forever + some extra bonuses like those ever-elusive naked pics of you, Tom.
I think a lot of the websites, that aforementioned VCs are currently throwing money at, do this freemium model?
(Reddit Gold being the first example I can think of)
I wish Newgrounds all the best.
The community here is awesome, and I know together, we'll help NG pull through!