I don't think the Spotlight is there to help us as creators, it's there to turn visitors into dedicated readers who will bring money to the site. They no doubt have considerable data on how well each Spotlighted title performs, and something that consistently performs well is bound to be brought back. It's not about what's fair or how much we want to be there - we'd all love to be Spotlighted - it's about keeping Tapastic healthy and active.
I did once see a comic return almost immediately after it had left (as in, within days), but it then disappeared again within a couple of hours, so I think that was a genuine error. Those comics that return every few/couple of months are surely there because they're good for business, though.
Personally as a reader I'd like to see less repeats because I like finding new things to read, but as a dedicated reader and creator, they don't need to appeal to me through the Spotlight anyway.