I lack the patience to go all-out on most pieces. That, combined with the tight working pace of making a comic, means I generally cut corners in order to create panels which look nice, but which certainly don't represent all that I can do. (Otherwise I'd be over-rendering every single panel, and I'd never actually have a comic I could share.) Sometimes I'll render a little more, if it's a panel I think looks particularly nice.
When I did have time to focus on standalone illustrations, I'd put a lot more effort into them. Especially those I'd identified that I wanted to make look as polished as I could. I have a few like that, which I'm still enormously fond of, but I haven't had the opportunity to do something like that for a while. The last one was the cover/thumbnail for Blue Star Rebellion.
I feel like if I did go 100% in an illustration now, it'd show a huge leap in skill due to the sheer volume of art I've created this year. Hopefully, I'll have a chance to demonstrate something like that soon!