You can make paying for sign-ups work for you, but you have to plan your strategy carefully.
First, you have to find a supplier for your sign-ups who isn't going to get your accounts banned. That means real, verifiable people who are going to sign up for the offers, and follow through to the conversion point of the offer.
Second, you have to get them at a decent price. The going rate (to my knowledge) is about $1 per sign-up. Not much point in paying $1 to get a $1.20 zip or email submit.
Which leads to: Third, you are going to have to find offers that will make buying the conversion worth your while. Which generally means either multi-field, or multi-page offers. Sure, you might get some people willing to fill out some offers from MicroWorkers, but they aren't going to be willing to do sign-ups like that for 10 or 15 cents. And most of those microworkers won't put in their real info or email, because they don't want to be bothered with the follow-up emails and such, which makes your leads un-verifiable, which is going to piss off the CPA because your Quality Score is going to suck, and eventually get you banned and possibly not paid.
Then, Forth, you have to get the traffic to make your CTR look legit. If your offer gets 100 hits and 100 conversions, the red flags aren't just going to go up, they are going to go through the stratosphere. So, now you have to factor in the cost of the junk traffic. Now your cost is going to be, roughly, a $1.05 per conversion.
Also, the vast majority of conversion suppliers will review the offer prior to agreeing to supply the conversions, and most will tell you that the offer must be a free offer, meaning the initial contact page cannot display a price, ask for credit card info, or any personal information. Subsequent pages can be sales pages, but not the initial page.
I've done this before, when I first started, to get some revenue rolling, and it can make you some decent start-up cash. I used education and biz-op offers that paid by the lead, and made some decent coin. I got lucky and had a friend turn me onto a conversion supplier that was reasonable on their prices, and had verifiable people doing the conversions.
If you are going to try it, I wish you the best. Just use your head, don't get greedy, and do your research.