The Hilton does actually have a shuttle van that will take you within a certain distance around the hotel so you may be able to use that route but if you can swing a car I think you will be better off.

As far as location from your conference I think the Hilton is not very far at all but you may look at the Hilton Garden Inn hotel in Old Town. It is a bit closer the some shops and restaurants in the Old Town area and there is a shopping mall not too far away as well.

I think either of those locations would fit your needs quite well. I just think that that cost of a taxi to either of them might be as much as a rental car and since you planned on getting one anyway.....