Can't argue that 9mm is cheaper than .38 Super if you don't reload.
I can tell you that I have two .38 Supers, a full-build Colt Lightweight Commander that was done 16 years ago and a SIG P220, and I love the caliber. If it were in my budget, I'd get rid of every semi-auto caliber I have in favor of .38 Super, starting with .45ACP. My Commander, with its Schuemann barrel is, functionally, the most accurate semi-auto I own. I say "functionally," because I have some old match guns and some new semi-customs that are all supposed to be very accurate, but only the Colt .38 Super regularly shows me cloverleaf groups (I have a GP100 10mm conversion that I use the same "functional" accuracy statement for in regards to my revolvers).
The drawbacks are ammo price and availability, but there are some good options out there. The Colt is very mild recoiling; almost a flat sensation when shooting, despite the Lightweight frame. The SIG has a bit more noticeable muzzle flip, but you can tell you're shooting something with a bit more behind it than the .45 P220. 9mm ammo has come a long way, but the .38 Super started with a 130gr bullet around 1300fps in the 1920s. Most current ammo is pretty mild despite the "+P" labeling, but SIG and a couple of others still produce ammo in the ballpark of the original loads.
You won't likely be disappointed if you add a .38 Super, but there are more common, cheaper, and similar performing cartridges.