I see your point; well put. I was also thinking along those same lines; DLC checks, title updates, etc.
Here are my results:
For Dead Rising 2 (6.1 GB), with all four DLC packs (psycho, ninja, soldier, sports fan), and with Case Zero; all title updated while connected to LIVE.
From DVD:
Start up (from dashboard to title screen) - 41.3 sec
1st load (title screen to first cinematic) - 20.2 sec
Load to 1st Platinum Strip cinematic - 31.0 sec
From HDD:
Start up (from dashboard to title screen) - 33.8 sec [7.5 sec improvement, or 18% decrease in time]
1st load (title screen to first cinematic) - 17.4 sec [2.8 sec improvement, or 14% decrease in time]
Load to 1st Platinum Strip cinematic - 27.2 sec [3.8 sec improvement, or 12% decrease in time]
I don't normally install my games to HDD, but since I've learned DR2 had ridiculous amounts of load screens practically everywhere (very true); I'd figure this exercise was worthwhile. Taking those 3-4 sec savings and multiplying them by their frequency and the net benefit was obvious. I also noticed my 360 was not as toaster hot, since the drive wasn't spinning like nuts. [this was my first full-game install]