Yep, my comic started terribly too... not just art-wise, but also generally comic-wise... paneling, dialogue (so much textwall and unnecessary rambling...), jokes/story flow ect. I don't really worry a lot about it, because my comic (on my main site) has the main page set at the last comic anyway (so first thing they see is where my art is at now, if they look further back in archives they'll know I have evolved from that). and my comic isn't a long-form where you have to read from start to end, but more gags and shorter 4-8-page stories you can read in any order (and for the news, well, I imagine many of them are less relevant at this point anyway...) Doesn't mean there aren't pages I want to redo at some point... especially ones where the joke is still good but the art is bleh. I actually redid a whole story a while back... because the old one was just bad, not just art-wise but also comic- and storytelling-wise.
For longform comics, they'll probably have to stick with the "bad" old art for a long time, but I imagine many webcomic readers will expect a comic, especially one that's been going on for a while, to constantly improve its art. If they see your newer update first, there might be a better chance they won't be discouraged by bad old art because then they KNOW this will get better after a while? For tapastic, maybe if you have an image in your "current style/level" in the comic banner, they'll at least see that and see what level they can expect and look forwards too later on. I really like to compare older pages to new ones and see just how much the artist has improved...
Plus, everyone is going to improve no matter what, meaning everyone will have "worse" art at the start. Unless you literally just copypaste the same character (ect.) bases over and over for years, you WILL improve, even if just slightly and slowly - and with that, your older pages will look worse in comparision either way.