I've had a G-20 for a long time and it is one of my most useful and well liked guns. But it is also for a very specific role. For just shooting at the range, or as a personal protection gun from 2 legged predators I don't think it is necessary. There are plenty of very good loads in 9mm, 40, 45 etc., that are more than up to the task for that use.
I spend a lot of time hiking and camping in black bear country. With the best loads my 10mm gives me power equivalent to the hottest 357 mag loads. I get a chronographed 1315 fps with 200 gr hardcast Double Tap ammo. About the same performance capable in a 4" 357 mag with equal bullet weights, and not too far behind 44 mag performance when fired from short barrels. My 3" 629 only shoots 240 gr bullets to 1150 fps and the Glock is still 3/4 lb lighter, an inch shorter and holds 2.5X more ammo.
The woods is the only place I carry my G-20. Even in the woods I still feel any threat is from 2 legged predators and having the ammo capacity of a semi along with the power of a magnum revolver in one lightweight package is comforting. In town, or when hiking/camping in areas where there is no possiblity of bear I carry one of my 9's or 45's. I like the 40's well enough, but since buying the 10mm sold them since with most 10mm ammo they are really duplicates.
I'll never tell anyone not to buy a G-20. They are great guns, but 10mm is a bit more expensive and harder to find. It is worth the effort to me,but not for everyone. I don't think 10mm is going to ever be obsolete but it will always be a niche round. It fits in a very narrow niche for me.