Well, i got into MF purely as a step-up from 35mm, and for me it has its place.
Started with aps-c DSLR, didn't go FF digital like i always presumed i would, instead I went 35mm Film so I could re-use my lenses I already had. From there I branched a bit, got 35mm Rangefinders for extreme portability when hiking (ie, camera in one hand, bottle of water in the other, car keys and phone in pockets, nothing else). It's slower than my (d)SLRs, but that's made up for in weight.
The other way I went is MF, pentacon 6 and hasselbladski, and mamiya 645af. The 6x6s are 'semi automatic', lightmeter on prisms, then manually adjust shutter speed and aperture. The 645 is even more auto, just point, focus, aperture priority, shoot. The 645 is not as fast as the 35mm, but IQ is better. The 6x6s are slower again but the negatives are a touch bigger, not having to tilt my hands to shoot 'portrait' with the 645 is enough to make it worthwhile (and IQ is exactly the same, I just use my 6x6 lenses on 645 with adapter).
I've just bought into 4x5 (yes, another Travelwide-convert). I'm certain that I will get much higher IQ than any of those systems just from the huge negatives/slides. I'm also well aware that I'll lose TTL metering, which every other camera of mine has (except a fixed-lens rangefinder with selenium around the lens). So that means light-meter and external viewfinder. Focussing will also just be a hyperfocal kludge, or an add-on rangefinder too.
So for me, there's a direct link between IQ, portability, and speed of use, and I'll take my horses to whatever courses demand it. Hiking long distances: Bessa and Velvia. Sports: 7D (maybe EOS3). Street: Bessa or EOS3. Driving and walking <100m: MF. Lowlight concerts: EOS3 (and f/1.2-1.4 lenses with 800 film) or MF (120/2.8 or 180/2.8 and Delta3200). Fun: whatever camera I haven't used in a while. Where the Travelwide(s) fit in I'll just wait and see, maybe it'll do Long hikes, maybe Short walks, maybe Street (personally i can't imagine street without Av and TTL, but I know a lot of people do, so maybe I'll learn). The trade-off there is going to be cost added into the equation too. MF costs maybe $1-2 a frame developed, 35mm 50c-$1. 4x5 will be closer to $10 a frame (my aussie prices for buying new Velvia and lab-developing, ymmv). So (at least to start with), LF is going to be a bit of a specialty, <5 shots on an outing, and I'll probably carry it alongside another camera for the more 'throwaway' shots.
I think you've already summed up where your hassy would fit, where you want more IQ than your F6 and can't carry an LF (and that includes enough holders for whatever you want to shoot). You sound like you're very adept at your LF camera, if you can use it almost as fast as your hassy, then you either need to learn to use the hassy faster, or just take ease-of-use out of the equation and focus on IQ vs Portability. Not sure if you're a pro when you say "my last shoot", if you're getting paid for this then cost is less of an issue, but for us hobbyists with day-jobs and mortgages, I just can't ignore cost-per-frame (i wish I could).