My pens are tools and are used accordingly. Writing every day with a fountain pen constitutes it in its way as a tool just as practical as a plane or a saw.
A craftsman will care for a tool - clean it, sharpen it, lubricate it, and so on. A well cared for tool such as either of the two Sheaffer MilClips in my pocket today can last seventy-plus years and still be used with great pleasure. I'm not running a museum, so I don't "curate" my pens, although with some of the discussions here at FPN on provenance for pens or the rejection of "Frankenpens", one might occasionally think that we're all working in some obscure academic museum.
I do have a few "specialty items" that don't get as much use, but they're still inked regularly and used - as tools.
As for collecting, I was given some extremely good advice by a local pen store owner many years back. He told me to pick a specific type of pen that I truly liked and enjoyed and then concentrate on that type. A type, I'd note, nothing so expansive as an entire brand, and so I decided in that period that I was most pleased with the M200 through M400 series of Pelikans. I "branched out" a bit to include a set of the 400NN series (green/grey/black/tortoise striped), and a Toledo; finally, I fell heels-over-head for the vintage Sheaffer Military Clips (MilClips) from World War II era, but only the 1000 and 500 series of these. I haven't tried to find every variation of the these various pen types, simply picking up the ones I've most liked. Others like Sargetalon, for example, have far more extensive collections of the M200/250 series of Pelikan than me, but, for my part, there are a number of those lines that aren't to my personal taste (although I frankly do sit in awe of Sargetalon's comprehensive collection of the M200/250 models).
I'll admit to getting a "back-up" of the Sheaffer MilClip 500 in carmine, as these are so scarce that I'd be hard-pressed to find one easily should the one in my pocket be damaged/broken/lost. It's incredibly doubtful that this style and colour will ever be "revived", so having one spare isn't such a tough decision. However, I don't have the same degree of concern for the brown/black/green MilClips, which are more plentiful in the pen world.
As for "completing the collection", I do look at the new models from Pelikan, but I've not been so amazed by them to acquire very many. I did perform a swap for the yellow highlighter/demonstrator M200 quite a bit back, soon after it was issued, but no new models since. The announcement of the new "cognac" M200 demonstrator model looks so close to the older "brown" M200 demonstrator that I'll probably not purchase it. OTOH, should an amazing deal on a lovely Pelikan arise unexpectedly, I might avail myself of the deal - that's exactly how I found a grey-striped 400NN arriving in the post months back, and then entering the rotation. As another tool, not a curated collection item...
I suppose that if I saw one of the hell-schildpatt/light tortoise 400NN models float past at a great discount, I might well consider it.