Increased valuations give him a much larger ability to draw on third-party loans to dump into whatever business he likes: the risk being if his investments don't pay off, he risks losing control of SpaceX.
[1] https://www.economist.com/news/business/21709061-entrepreneu...
Additionally - I don't know where price-wise Musk gets margin called on his Tesla stock, but I do think him borrowing against it is a significant risk for Tesla. In my personal opinion, Tesla's biggest asset is Musk's fan base - I think it would really significantly impact Tesla if Musk got margin called and couldn't (or doesn't) cover and lost his status as the largest shareholder of Tesla. I think he would lose more interest in the company and you risk his fans no longer seeing Tesla as "his" company.
I don't think I'm alone in this opinion either, Musk has borrowed enough against his shares to warrant getting margin called mention as a risk in the 10-K. (Not to say its wrong for him to borrow against them, I'm sure I would do the same - I just think doing it to fund a private company he is heavily involved in (and distracts him from his public company) links them financially in a way I would personally not be comfortable with if I were an investor in Tesla).
[0] https://electrek.co/2017/04/14/tesla-solar-bonds-elon-musk-s...
What was paid back were "Solar bonds", which were not SolarCity bonds.
I can see why you would think that though - the PR around that only mentioned what they were paying early, not what was being inherited. (I think by design, but I have a cynical view of Tesla's relationship with the truth so that's only an opinion).
[0] http://fortune.com/2015/08/07/this-is-why-elon-musks-spacex-...
(EDIT: I was agreeing with you on the details, but also pointing out that there are effects here beyond the money directly raise that could help Tesla.)
Tesla will do a minimum of a $2 billion funding raise whenever they need to next. They're claiming they won't need to do a funding raise this year (we'll see).
The SpaceX capital would be far more likely purposed to help pay for BFR & Starlink.
edit: downvoters want to clarify what's wrong with what I said? It's extraordinarily obvious the $507 million raised by SpaceX isn't going to bailout Tesla. Mathematically it couldn't even if they wanted to put it to that use.