Hmm, @doc toothache made a good point.
Since you are reapplying, why are you considering now to shadow more? Is it because you think you didn't have enough hours during the previous cycle?
A minimum of 100 hours shadowing hours is recommended... 200+ to me seems a bit excessive (do you not die from boredom?), but it definitely doesn't hurt to have more. Anyways, you mentioned that most of your hours were from a specialist. That could be a problem as most schools want the bulk of your hours to be from not one, but a couple or more general dentists. Certainly consider this if you plan to continue to shadow.
Anyways, back to your question. Shadow or assist? By all means, assisting will give you much more dental experience than shadowing ever will. Heck, when you assist, you are technically shadowing, so why not just assist and get paid while you're at it (you're killing two birds with one stone here)? But assisting isn't for everyone as it might not be easy to find a job if you're not certified, which takes time and money to get. Once you become certified, you'll certainly want to work for a while or even be expected to work for a while, so definitely consider the commitment for that.
Anywho, take your pick and...
Best of luck~