Why does the 180 cost $100-$200 more than the 175? Is that 5 amps extra worth it?

I don't know about the hobarts, but with the lincoln 175 and 175plus it is extra for the infinite amp control. Not just 4 or 5 taps to use, you get a full range with a rheostat. I think the full control is better for me. I even got the 175plus for less than the hobarts, $700 for the hobart plus shipping, lincoln SP175Plus at lowes $649.

the 175 was discontinued a couple years back and most of the time you find them they are refurbs (not that, thats a bad thing)

mine (Hobart 175)pisses me of i started with 030 gauge and didnt work well so i tried 025 still doesnt weld very well i have found the 250 is worth every penny i can weld most material and by changing wire diameter it works on sheetmetal all the better

best of luck

Yep the 180 is simply newer, it does not have infinate amp control, but it is (or should be) cheap. i paid right around $500. for mine on sale gas ready.
I bought it as a step up from my old handler 135, I should have stepped up farther.