This guy already has an 11-32 with a long-cage derailleur. Why should he buy anything new? His bike works.

Likely if he got the SS he would need to fiddle with the B screw and Possibly have issues with too short a cage anyway. So ... possibly he would need to buy both a derailleur and an 11-28 cassette to get back to where he is now.

[MENTION=392454]CliffordK[/MENTION] raises some good points. If this person in primarily interested in keeping up on group rides ... either he already is or he already isn't. And, he is either using the whole cassette or he isn't.

If he is not using the top couple cogs, then he Might want to get a closer-spaced cassette. It Might make his group rides easier because he Might find it easier to find the perfect gear for his fitness level and the speed of the peloton.

Or he might end up buying a cassette and noticing no difference. I ride both 11-28 and 11-32, and there are plenty of close enough ratios in there, for my needs, Everyone's needs vary. These are things the OP needs to consider.

I do notice that at no time does the OP seem to want to replace his cassette, in which case the answer is simple: NO, do not replace the derailleur.