"I really don't know how you envisage a ST that uses minimal SPFX"
B5 managed to do SF on the cheap in the relative dark-ages of CG. How much do you think it would cost to do B5 with today's computers? You could probably have a render-farm with 1/10th or fewer computers than were required back in the day. I understand perhaps the main cost of doing FX is manpower, but still, the fact that you have Trek fan films that employ virtual sets and have space shots that are actually better than the standard def stuff we saw in the TNG era should tell you that it doesn't have to cost what you think it has to cost.
I don't know where all the money goes with these big-budget things, but I can tell you that the money just isn't being spent wisely. It's being put into rendering details that are, for the most part, superfluous, doing things digitally that could have been done through compositing live action (like water or blades of grass). Trying to do 3D dolly shots in all virtual alien environments that used to be done with simple 2D matte paintings. All these things are done purely because they can, for the novelty-factor and the bragging rights, not because they are the most cost-effective, but they have the net effect of requiring an army of technicians rather than a small crack team. There is a point of diminishing returns as far as adding more and more visual detail. Because we don't have a lot of modern reference points for things being done on the cheap, one can only speculate, but I believe that you can maybe get to 80% of an optimal entertainment experience with a low budget as you could by spending 10X more to get to 100%.
If you want to say that Trek is still a tired franchise and should only be trotted out as big-budget tentpole films, fine, but I just think the budget argument is bogus.