I was racing on Bowser's Castle and before the race I had just under 9000 points.  I crossed the finish line in 1st place and as soon as I finished I was disconnected.  When I reconnected I found that my points had dropped to just over 8500.  So effectively I lost around 500 points as a result of my broadband connection.  I think this is totally unfair given that it was in no way my fault and most importantly I had already finished the race in 1st place anyway. 

 If I write to Nintendo to tell them what happened do you think there is much chance my points would be restored.  I know the points don't really do anything but I worked hard to get over 9000 points and not too pleased about losing 500 points.  Plus having a high score puts the fear of God in other racers before the race starts.

There's about zero chance of them adding your points back. They are lost forever but 8500 is still impressive and you'll be able to climb back up to 9000 if you've done it once already.

It is your connection that is the problem therefore you lose points, there would be no way to prove to Nintendo you didn't simply pull the cable out of the router.

It's tough luck until you get a better connection.

Personally I have the cheapest router I could find (Belkin wireless-G. £40) and it works just fine.... I have only been disconnected due to my own connection 3 times.... Once I lost about 90 points as it was early on, once I was in a team vs after one of the European GPs Ben set up, and the last time I unfortunately lost 350 points due to it... so I have had to build them back up since.

I had one diconnection so far and I prefer blame it on Nintendo's servers.

Do it hard buddy.

I have thought, that it puts you back where you started last time when you have a disconnect.

I'd be around 9000 too without the disconnects, and above without losing.
Few times i've had disconnect because of server lag and few times because of my ISP.

Yeah, you're just complaining because you got busted from cheating and lost your points. If i recall, our record looks like you're a cheater. Edit: Yes, definately a cheater, you have 4 wins more.

The points will stabilize back into the 9000+ range if that's your skill level...

But the fact I had already finished in 1st place shows I didn't do this (I would be insane to).  I think Nintendo monitors online races to check out for cheats.  So maybe, just maybe there could be a way for them to check to see I had already finished in 1st before I got disconnected and as a result of them feeling generous they give me the points back.

Hahaha no.
But I feel your pain, it has happened to me at least 10 times already. It's funny, there's different kinds of disconnects: Sometimes I get this error code, sometimes it says "disconnected from other players", sometimes it just quits. I lose a few hundred points everytime. A good friend of mine always gets awarded first place and a lot of points when his connection fails. Don't ask me why.

What you see on your screen isn't necessarily known by the server. In most networked games, the server is always a few frames behind due to the techniques used to ensure lag-free play (the game responds immediately to your actions, but the server only receives the information some time after).

The bottom line is that you probably had crossed the finishing line on your screen, but Nintendo can't necessarily check it. If the connection was dropped before you crossed it, there's no way for them to know it.