The WCL just gives you that extra bit of width, I find it useful on things like city breaks, town visits, etc, where you don't always have the option to zoom with your feet. Given it's size and potability it's really easy to slip into a pocket.
And with the addition of a cheap (£10) 49mm fisheye adapter, with X100+WCL you can get a full circular fish-eye!!
170819 Liverpool Museum Fisheye X100F by
David Yeoman, on Flickr
I totally agree about it focusing the mind with regard to other kit. I'm having a daily battle of what to keep and what not to keep. My current struggle is with Samyang 8mm, Samyang 12mm, XF14mm and XF16mm, which 1,2 (or 3!!) do I keep, and does anyone have a crystal ball to know what the forthcoming XF8-16mm is going to rush me, and if I take that option, I'll need a whole new set of filters (currently have about £600 worth of Hitech Firecrest)..... At least you can never accuse this hobby of being boring.....