Update:

The PlanetX XLA-SL now has 6,435 miles on the frame (and most of the components are still intact), and the ride is as good as ever. The first thing to wear out was the cross-oriented rear tire -- not at all surprising; still, the Panaracer Comet Hardpack survived over 3,000 miles. I traded out the front tire soon after, but there was still some tread left there (switched to Continental Tour Ride, bog-heavy and stiff as nails but indestructible).

Around the time the tires went out, I decided to start digging in to other parts -- namely the hydraulic brakes (which I had no prior experience with, except for motorcycle systems). I splurged on the SRAM Pro Bleed kit, and was impressed with the syringes and fittings, which made for a mess-less procedure. After the bleed, the brake levers were more symmetric in their feeling, and just a bit firmer than from the factory. The front brake pad was changed too, but the rear still had some life left in it (it's starting to squeal just a bit, now -- it's on the list for the next major maintenance day).

I am surprised by the chain, which has yet to reach the 0.75 mark on my chain-check tool. Either my check-tool is bad, or the chain lasted far longer than I'd expect. I'm not a big sprinter, and I've been meticulous in my lubrication (especially after gravel rides). In any case, a fresh chain is waiting on the shelf (and a new cassette, just in case).

There's been very little adjustment otherwise, perhaps a few twists of the derailleur barrel adjusters that I've lost count of along the way. There's a few new creaks here and there, possibly the bottom bracket, or just dirt working itself past the seat post collar. The whole bike is due for a deep cleaning.

I've customized it a bit to make it more comfortable. The factory Selcof seat had sharp edges for my thighs; a cheap Charge Spoon was an easy enough replacement, and good enough for century riding. I've added some more capacity than most (partly to avoid resupply stops amid a global pandemic); a Carradice perched on a Bagman has been enough to add 1-2 liters of water, and enough food for a full day out.

All in all, the bike was a great investment, though, as an "enthusiast", of course, I'm still scoping out a few things -- carbon wheels, perhaps, flared drop bars, a 'feedbag' for the cockpit -- but none of that is essential. A real shame the aluminum version is no longer available, but for any interested readers, the XLS Evo Carbon looks to be much the same bike.