The demand for the Maxi's is there. But only you can decide if you want to "invest." Here's a few numbers to consider.
There were about 16314 of these guns built. However,, Bill got pizzed at the few complaints about flame cutting and stopped production & scrapped approximately 5000 guns. That leaves somewhere around 11000 guns.
Many folks who want a "different" gun, use the Maxi's as the base for a custom build due to the longer cylinder window.
Through various discussions,, it's estimated that somewhere between 1000 & 2000 guns have been customized & are no longer a .357 Maxi. That leaves 9000-10000 guns out there. Maybe.
Then there are the collectors vs shooters.
Many are already shot,, and a smaller percentage of them are ANIB.
So,, as for an investment,, your call.