I think you are very wise, Rhys.
Purines are relevant to gout. But, everything has to be put into context. In your case, it’s your 95% vegetarian eating style. I love that phrase as an alternative to Mediterranean diet. I’m going to use it when I describe a sensible approach to healthy eating.
Purines in the context of healthy eating are never very significant. We can never avoid purines completely until we become skeletons. Human flesh is the biggest source of purines, unless we have a truly unhealthy carnivore diet.
So, as you say, “How bad can tiny amounts if these be?”
The answer is, not very bad at all. Certainly not worth worrying about.
One important consideration is that purine foods rarely trigger a gout attack. Gout attacks come from the millions of crystals that have built up over months and years. Managing that comes down to keeping uric acid at safe levels. That means, getting uric acid blood tests at least once a year.
Until we get rid of most of the old uric acid crystals, we always risk a gout attack. There are lots of things that can trigger a reaction to those old crystals. I don’t think a few seafood purines are going to make much difference. You could negate their effects completely with a glass of milk with your meal.