We also had our account blocked last year but they never told us why. We don’t sell anything via our newsletter. We don’t even talk about how to make money (that’s not our field). We write about business news and part of our CRM initiative. We sent several email inquiries to them. All were ignored. We ended up setting up a new account and reimporting all of our lists.
The only other thing I would have mentioned under design is to not underestimate the power of colour and textures – in my hunt for a theme that I actually want to work with, I’ve narrowed it down to finding a minimalist theme and just giving it a hint of colour to add some flair. Otherwise things can just detract from your content just like you said.
Check your ‘Form Type’ settings to alter the width of your signup box. This is important as you need to make sure that it is the right size for your site. Think about where you want the box to appear on your site – for the sidebar, you will want it reasonable small (perhaps 250-300px wide) whereas if it’s for after your post, maybe something much wider (e.g. 600px).
Think about implementing referral links to incentivize your subscribers to spread awareness about your brand, too. Referral links allow your current customers to promote trackable links for your business. In exchange for sending new paying customers your way, you can give them incentives like discounts, coupons, vouchers, cash, prizes or redeemable points.