Horsepower is always welcome! If I were to want more, the TCM IO-360 is what I'd do also. But some things to keep in mind is:
1. You'll have less endurance due to increased fuel conumption. (You may want to consider adding aux fuel tanks.
2. You'll have significantly better takeoff/climb but not as much gain in cruise speed.
3. You'll be a committed 100LL avgas user. The IO-360 is not approved for autogas.
4. You may have to relocate your battery aft of the baggage compartment to adjust the new Wt/Bal.
A 170 is very sensitive to weight. Over the years they gain a few pounds. (Don't we all?) If you can get rid of old wiring, old inoperative/obsolete radios, unneeded "junk" you've become accustomed to carrying under the rear seat that you've forgotten about,...you might be surprised to see a significant improvement in your rate of climb. Some 170's have empty wts nearly 200 lbs more than others, simply due to weight gains that have been allowed to accumulate. It makes a big difference on those high density altitude days, and it's a lot cheaper to put the ol' girl on a diet than give 'er a sex-change (high-testosterone engines.)
But I understand the desire. Like one of my buddies was once heard to remark,....(although specificaly he was referring to boats, ...the idea is the same.)
"Engines are like anchors and bilge pumps and bikini tops..... The bigger the better!"