I've used both the d200 and the d300 to shoot weddings, and the d200 certainly produces great photos. The difference between the two cameras is that the d300 improved on all the rough edges of the d200. Consider:

1. The D300 has one stop better noise handling. I feel comfortable shooting up to ISO 800 on the d300, 1600 in a pinch. Halve those numbers for the D200.
2. The D300 has the same basic controls as the d200 (ISO button, quality button, etc) but everything just felt far more streamlined.
3. D300 has 'live mode' (which I very rarely use).
4. The D300 has much better battery life than the D200. When I'm traveling, I can have two batteries for the D300 last for several days (3 or 4), which is handy when there aren't many outlets nearby. The d200 batter lasts for maybe 1/3 the amount of time (meaning I need about triple the number of batteries to last the same amount of time).

Having said all of that, the d200 is a very capable camera, and a definite step up from the D70 I used before that.

As for starting over, well, I guess the important question there is budget. If you're not comfortable going for a d300 in price, I'd imagine that swapping out your lenses for a new set of primes would not be cheap as well. I would say that using manual focus lenses on a DSLR is not easy, because the crop factor makes it difficult (at least for me) to focus easily.

If your son's judo is a priority, take a look at this question here: Fast prime vs. expensive zoom for indoor sports photograhy?

Depending on the lighting, the d200 coupled with your fast primes will almost certainly be able to handle the load. Being able to shoot 5fps in burst mode also helps.