We just got back yesterday from a 10-day trip, driving from Holland on a Monday evening to fly out Spirit early on Tuesday am. We stayed at the Howard Johnson (formerly Quality Inn) Metro Airport on Merriman. We got one night in the room plus 10 days parking (and shuttle to/from DTW) for $85.00. It was a little noisy with planes going by, but it didn't bother me at all. The room was clean and there was a nice breakfast in the morning (juice, coffee, patries, waffles that were GOOD, fruit, etc...). The shuttle runs every half-hour and worked out great. Upon our return (8:30 pm), we got all of our bags then called HoJo and told them we were at the Spirit baggage claim. The shuttle was there within 10 minutes. I had no problems whatsoever.
The only issue would be the noise of the planes flying over. The HoJo is set up with about 10 one-story buildings, so there aren't multiple floors to muffle the sound. Some of the park-and-fly hotels are multiple stories so maybe more quiet. I guess you get what you pay for - HoJo was the cheapest I found but was absolutely adequet for us.
All in all, I'd do the park-and-fly at HoJo again.