Do you like core D&D, and see no reason to change? If yes, then buy the mini's, or even better some Fiery Dragon Counter Collection (under $20 for hundreds of counters of all types, exactly sized for a battlemat).
If you wish to buy AU for totally different campaign setting and different take on classes, races, feats, and spells, then go for it. If, on the other hand, you wanted AU just to steal the occasional spell or class from it, I don't think it may work well for you. AU is a GREAT game, but it is far better off taken whole cloth than piecemeal, in my opinion.
Any more info on the appeal of each purchase to you? We might be able to help you better.