"I am under the opinion that bullet expansion is important to the reliable, effective taking of game but I would like to hear people's experiences on the subject."
I agree with this 100%.
There seems to be universal acceptance of the expanding bullet otherwise there would be no expanding bullets manufactured. There are many compromises that must be made when making a bullet. These compromises greatly increase in number and complexity when designing a hunting bullet rather than just a paper puncher.
Is expansion necessary in all cases? From personal experiences I have to say no.
Example 1) Raghorn bull elk @ 120 yds. Cartridge: 223. Bullet 60gr SMK. One shot. a few steps and DRT. Bullet retrieved from very low in the rib cage didn't even get to the skin on the far side. There was no deformation of the bullet except for the rifling.
The tip of the heart was removed opening both chanbers.
The whole deal was a fluke. Kid got the fever. It should have been a muley buck but those antlers looke reasonable for a great buck above the top of the large bush.
Bullet performance is fully documented by the ID F&G.
Example 2) Local high fence operation fills orders for elk meat with a carefully placed neck shot from a 22 LR.
Example 3) I recall a story from decades ago where a noted writer wanted to scare a bull moose so a visitor wouldn't see it or something on that order. Maybe it was Col. Townsend. Anyway the moose was a couple of hundred yards away or so. A 22 LR was randomly stuck out the cabin door in the general direction of the moose. Long story short, 1 dead moose.
Nevertheless bullet expansion is a great early innovation regarding hunting bullets.