Sorry but aluminum absorbs and disipates heat nearly as fast as polymer and also expands and contracts, depending on the alloy.
If you want a quick accuracy upgrade then buy a 6" by 1/2" Picatinny riser block and bolt it down across the gap between the polymer upper receiver and the the polymer quad rail handguard. By locking the mass together it stabilizes the rear of the barrel. Better solution would be to get 2 thin steel plates and put them on the flat vertical surface below the upper rail, and drill both them and the polymer underneath to lock the area even better. But the best solution is to replace the polymer handguard with a metal one (or carbon fiber). Then the barrel nut will be locked into a long alloy section that will better stabilize the barrel by locking its nut to a larger metal structure instead of just an alloy collar nut holding another polymer structure.
Yes both an alloy upper and lower would help, as long as the barrel is good. Otherwise just go build an AR lower and buy a .22 upper assembly, assuming it also has a good barrel.
I saw one of those shooting the rimfire side match at the PSA Shootout over the last 4 days. Shooter was sponsored by Lancer Systems. Don't know which upper it was but it did use Black Dog mags and had a carbon fiber handguard on it. However most of the bigger shooters were actually using modified AR15-22 PC and regular models (after all S&W is the main match sponsor for this event). Plus the usual assortment of 10/22s, usually by junior shooters.
I had the 3rd best score after the first 3 days of the 4 day event at around 60 seconds. That is 70 targets, some only an inch in width from 8-25 yards, plus 2 Texas Stars and 6 plate racks of various sizes all had to be shot down within the 90 second par time. I managed to dump 4 complete mags in that 60 seconds but it took me shooting 100 rounds to get all the tiny targets. I was using my usual TruGlo dual color reflex sight. Some used tactical 1-? scopes. For this I am not sure which was better.
This was a sample of their 3rd annual PSA Rimfire Shootout the last week in October. They have changed the name to the PSA Rimfire Challenge. It will be over 2 days unlike the first 2 two which were 1 day events. Divisions for open and iron sight pistols or rifles and 2 person teams with one shooting rifle and the other pistol (both must be same division either iron or open). It will be 4 stages of a combined 200 steel .22 knockdown targets around 50 per stage. It will be fun.