Some folks go nuts with engine mods, to the point of making the bike less reliable and causing drivability issues in "normal" riding. There's a happy medium there somewhere. I had a '06 SEUC with the 103...pipes, A/C, and a good tune was good enought for my purposes. Had I been able to keep that bike, I would likely have installed some kind of drop in cam when the chain tensioners were due. But it's gone. Now I have the '11 SERGU and my main use is two up riding, with some trips thrown in when we can afford it...neither of us are large people, so I am happy with the Fullsac Stage I system I installed. Those simple changes made the bike "feel" better, and improved drivability. A more efficient cam would be nice, but not necessary for my needs at this point in time. If I need more power when riding, I just drop it down a gear.
My "thing" on a bike is handling and ride quality. So, I invested 3K in suspension improvements, and for me, that is money well spent. It makes the bike more fun to ride in every respect. So does HP/TQ, but within reason, IF you actually use the bike for touring.