I am afraid that my answer is going to be tainted by the fact that my DW and I shelled out for the half in January, but I thought it was a great experience. We had multiple reasons for being there, so we didn't go just for the race, but we had had it on the calendar since my wife started running (and I started running again) around this time last year.
From your perspective, it would be a fairly cheap runDisney race, because you would a) be down onsite already, and would therefore not have additional transportation costs, b) all the resorts should be host resorts, so no matter at which resort you were staying, you could get a bus to the starting line, so the PP's suggestion about switching to a less expensive resort (and, compared to Theme Park View Contemporary, most of them would be), makes a lot of sense if you're worried about that outlay, and c) you will be in time to get the early sign-up price for the half-marathon, the sign-up for which will open shortly.
So, compared to planning a whole trip around a different race, you will have already put a lot of money toward getting to WDW and getting acclimated, so the extra money for race registration and a room for an additional night, although expensive, might make sense if you'd like to add a runDisney race to your list of finishes.
