I actually had a very similar setup to you. I ran a 202 with a TeddyCAP+ & the 150X & was pretty happy with the setup. I added the TeddyCAP+ first as from what I had read, the external power supply makes the biggest difference & many had said there wouldn't be much change in the different Naim amps (unless you had speakers that are particularly hard to drive). The TeddyCAP did make a pretty nice jump in sound, but to be honest if I had paid what Naim wanted for the HiCAP, I might have been a bit disappointed.
I was looking to upgrade & to be honest I liked the look of the 200 better then the 150X as it matched the 202 casework & I figured the 200 is the natural partner so might as well make the swap. To be honest, I wasn't expecting much change but after listening, I was almost shocked at the difference. The 200 was as big if not slightly bigger then adding the TeddyCAP+. Bass control is far better, it does remove some of the upper bass boom but get the right track with really low bass & you'll wonder "where did that note come from?". The clarity of the 200 was far superior, as well as all other areas being a step up.
Now, I believe the reason for my experience is the order in what things were done in. When others add an external supply that already have the 200, the 202 is the weak link so adding the PS really improves performance. In my case, I believe the 150X was sort of the limiting factor. So when the PS was added, I wasn't getting the full effect. When I added the 200, I got the effect of 200 itself, which in turn allowed the PS to give its full effect.
If you haven't tried it, I would definitely recommend giving the 200 a try, you might be surprised. I run Audio Physic Scorpio's, & their not an extremely demanding speaker, so it wasn't a case of the 150X not being up to the task of properly powering my speakers.