Big companies, your nike, wall mart, netflix whatever pay a lot of money in research.
What about us little guys, thankfully if you dig deep enough you can find some tasty brain nuggets. Get out your pocket protectors and reading glasses this is going to get down right nerdy
Opening course: Increasing conversion rates: Top reasons people fail to complete a checkout process resulting in sales, and what we as store owners can do about it.
http://baymard.com/checkout-usability
Classroom: Five Essential Principles of Interaction Design
This tells us that navigation on the interent isn't as easy for noobs as it is for others.
http://adobe.ly/yPj12G
Making it easier to buy, means re engineering your information to be clutter less.
http://www.siegelgale.com/white_paper/2011-global-brand-simplicity-index-united-states
Ok with some data to back this up, I think the best investment for storenvy moving forward would be to get rid of the form, ( I think this is the highest point of congestion in the current process, and leads to the highest number of "See you laters" maybe you could use Facebook connect to do this, or get that data earlier in the signup process, and save it, (not as scary as it sounds, everywhere saves data) so it's not a hurdle during checkout, or offer paypal one click payments, Paypal already has my shipping information why enter it twice.
Part 2. Themes They have been coming soon for a long time.
Large pretty product photos, and well displayed information.
See the custom store post for how this works.
I'm not saying rip off those stores, but make a better theme designed for all to use, to move folks along with products rather then just move them along.
Strengthen differences. Promote more.
What makes Storenvy special and attractive to sellers, and shoppers?
Why are people still using Big Cartel, Etsy, Ebay, to sell stuff?
Get them in here. Bang pots and pans to do it if you have to.
I understand it's a small team with limited resources, but with precision execution you have more then enough to make a real impact. You only need one bullet to hit a bulls eye if you got the right scope, no matter the distance. Hit it!!