I really want this item!

The short answer to your question is "no." A bid you place and a bid AS places on your behalf are identical. They are both bids by you. Thus, you will only be liable for the amount necessary to win the item no matter what your max bid is or where it came from. I use your technique sometimes when eBay is in a slow mode, just so that one bid or the other gets placed.

Speaking of slow modes on eBay, a couple of days ago there was a slowdown and I couldn't access eBay from my browser. But I could access AS easily, and found that there was no trouble in getting to the items I had set up for snipes, even though "moving around" in eBay was still very slow to impossible. That's something to keep in mind when an eBay slowdown hits just as you want to watch your snipe and perhaps modify it. With AS, no problema.

Thank you, Steve.
I had heard about the eBay slowdown. I had read if a person had another way to get to a listing rather than eBay homepage, they would be fine. I immediately thought, aha AS. I didn't have any listing that I needed to watch out for, but thought if it should ever happen again (which I am sure it will) I certainly had a distinct advantage over non AS bidders!