I helped a friend build a pair of 2Pi Towers a couple of years back. They're tower speakers, with high sensitivity drivers. The build is a rectangular box and a rear port without a tube. Just the thickness of the mdf used for their construction. A very simple crossover. And they sound dynamite. My friend had been using a pair of Technics 2 way budget bookshelf speakers he'd had since a teenager. The transition to these was staggering.
I'd built a pair of Pi horn loaded bass reflex speakers years before that are BIG and sound BIG. I use tube and solid state amps with it. High sensitivity speakers have quenched my desire for fidelity.

I'm kinda puzzled with what "parts" wear out with DIY speakers, anymore than commercial speakers. Capacitors, coils, resistors or speaker drivers? Many DIY speakers I've been familiar with usually use very good speaker drivers as well as the crossover components. And DIYr's tend to overbuild their cabinets to the commercial ones. About the only thing I can assume is that many people aren't DIY oriented is from cabinet construction and I guess sweat equity goes into building DIY speakers.

But for me, that was the compelling challenge. That and the cost to performance ratio. It's all good though in enjoying what the audio pursuit is.