I'll chime in as for the focal length part of the discussion, I've always felt the need for a long lens, especially on landscape shoots, even if just to have something to turn to after the hero-shot or if the conditions do not allow for the hero-shot which, in my case, is often a wide angle, all encompassing kind of image.
I can't comment on the SK 240, but after considering the 2x teleconverter to be paired with my 150/2.8 I decided to opt for the Mamiya 300mm f/4.5 instead. It's a light lens rated at 1430g (50.4 oz.) whereas the SK 240 is rated at 1600g (56.4 oz.), so it basically has the same max aperture with a bit less weight and 60mm longer focal length (size wise, the Mamiya is a bit longer and thinner).
Sharpness of the 300mm is more than good enough for me, stopped down for landscapes it's as sharp as anything in my bag and interestingly, on the IQ3 100mp, the Mamiya is sharper than the famous and outrageously expensive Hasselblad / Zeiss superachromat 350mm f/5.6, at which I was pleasantly surprised (perhaps I had a lemon, I don't know).
Anyway, just sharing my experience so you have another option to think about and I'm pretty sure the Mamiya can be had on the second hand market for much less than the SK 240.