It used to be okay to collect email address with iframe but after the module is spammed for 5093 times, Squidoo decide to stop allowing the use of iframe. But yet, I believe you still can do this now, not directly on Squidoo lenses but by directing Squidoo traffics to your webpage that collects email. A suggestion of readings: http://soufulow.com/online-biz/how-can-squidoo-bring-in-more-traffics-for-you/
Yup I have built a responsive list from Squidoo lenses. What I did was set up a blog, and have an opt in form on that blog, then add my blog rss feed to each lens. Next I fitted each lens with an out bound link to an opt in or squeeze page for a free gift in exchange for their name and email. The free gift was in relation to the topic of the lens and was usually a PDF file or resale rights product. The next step was to draw tons of traffic to the lens, I detailed all that in the lens below: http://www.squidoo.com/traffic_building This lens was in the top hundred for over 150 days and held a top position of 8 overall and was #1 in affiliate marketing and SEO for months. Enjoy.
The question sounds a bit weird to me... yes, you do get extra traffics when you're in Top100, but you can only be Top 100 whenever your lens are doing good in popularity. Squidoo Top 100 are in the top 100 because of the amount of traffics they pulled in OUTSIDE of squidoo. thus, it's frankly hard to tell how much traffics you can receive from being Top100. It's like asking how much traffics your blog can receive - the correct answer will be always: unlimited (as long as your server doesn't crush). Thus, as said, being in Squidoo's Top 100 doesn't mean you'll have a big % spike in traffics; but being Squidoo's lens of the day will!
I have an exception to that rule: My lens www.squidoo.com/basichtml gets fewer visitors via search engines then what it pulls from within the site. It's been in the Top 100 for 200+ days.