Well - the older Wingmaster probably has a fixed choke - likely full. Thats the big disadvantage over a new shotgun with removeable chokes. As a minimum, you will have difficulty shooting steel shot out of the full. And a full choke is sub optimal for upland game hunting, and sports such as skeet.
Why would you think that? Old Wingmasters can take any 870 barrel, just the same as any new 870.
I have an older Wingmaster in 2 3/4, and its fantastic. The quality is superior to any piece of junk 870 Remington puts out these days.
If the one the original poster is buying has an adjustable choke , go for it. Magnum and Super Magnum shells are overrated.
None of the ducks, grouse, rabbits, and other assorted small game I have shot with mine have ever complained (being dead and all).
I also would have no qualms with shooting a bear, turkey, or deer with it.
The only time I would consider upgrading would be if I were to get seriously into goose hunting. For now, it'll kill the goose, just wait for it to come in a little closer.
Shooting ducks, put in a mod choke. For grouse, try an improved.