I would give the pump and impeller a thorough cleaning with vinegar and a toothbrush.
Make sure the air intake and associated plumbing and fittings are clean too.
If that doesn't help, I think it's hard to argue against getting a replacement for what's broken - usually just an impeller.
At most, get a new pump that's the same model as your old one.
"Upgrading" the skimmer is an unlikely scenario if it worked well to begin with - it won't get better, it will get mor finnicky - so spending a bunch of money on an "upgrade" isn't a good way to go IMO. If needed, either replace the impeller or the pump with a direct replacement, or if you really want to get something new that would be an upgrade...
Spend $325 on a Tunze 9415. Great skimmer, easy to own, very compact, works like a beast, has several unique features.
But again, if all you have is a cleaning to do or a new impeller to try out....