Do subwoofers really help?

I think a sub is a band aid in the scenario outlined. The right approach (happy path) is to fix the speaker/amp mating first and go from there.

Yes, especially dual units.

What is the nature of the 'mis-match'?
Impedance of speaker too low for amp?
Phase angle problem......amp can't produce enough power?
How can you tell there is a problem? distortion? Smoke/flames?/ Neighbors complain? Dog leaves room when you start the Stereo?
How did you end up with this combination? What's going to prevent you from doing it again?

Fixing this problem by buying MORE stuff is probably not the answer. You can do as others suggest, add complexity and drive yourself nuts with fine tuning / messing about. OR..... get a proper amp if you love the speakers or proper speakers if you love the amp.

Perhaps you should contact Paul Speltz regarding the autoformers before you make any big steps. I have not tried these, but I believe the purpose of them is related to your issues. Based on my assumption that the impedance curve of your speakers combined with their sensitivity and amps' dampening is creating the problem. I don't own or use the autoformers or zeroformers, but I think this is what they are supposed to address.

No, it's smarter to get a better amp. Why would anyone try to match speakers to an amp?

I find speakers I like...and then buy the amp they need (unless my current amp works fine with my new speakers).

Of course, if you have a good pair of speakers, and an amp that can handle their load with ease....adding a subwoofer (or two) is going to make things easier on all components involved....less work everywhere, and more options on placement (the best sound for mid/highs, is not always the best placement for bass reproduction)

Dave