I think the idea that Doctor Who would benefit from a much bigger budget is maybe an unfounded one.
As a family show that skews pretty low in terms of its youngest viewers, it’s always going to have a different approach than a more adult sci-fi show would take. The baddies and monsters aren’t meant to be things that are genuinely disturbing and scary for adults - they’re often slightly cartoonish creations that are more suitable for a family audience.
I think it’s tempting as an adult viewer of DW to judge it on the same criteria as other adult shows, but it’s not really trying to do the same thing. I’ve watched quite a bit of the show with my kids (the classic series and the RTD/Moffat years) and they enjoy it for the ideas, regardless of whether the effects are a bit shonky or the sets are a bit artificial - and in fact, for the scarier episodes, that slight shonkiness helps to reinforce the idea that it’s not real and it’s just a story.
I’m not saying the effects couldn’t be better - there are times when they look a little rough, especially compared to TV shows that have millions spent on them per episode, or big blockbuster movies - just that I don’t think it matters that much for a show like Doctor Who.
I think it’s particularly impressive that the show looks so good (and so much better than even a few years ago) given that the BBC are reportedly spending less money on it these days.