My nc30 has an original exhaust in excellent condition except for the collars where the clamps connect under the fairings down by the sump. Is it worth getting these repaired or better to get an aftermarket exhaust fitted with more places to split the exhaust in the future?

thats the only part of the system that will rust out, you can get the collars replaced with some stainless steel and theyll last forever pretty much.

rcv4 a member on here is a professional welder and used to offer a replacement service if your stuck with where to take it, top quality work and good price.

Depends on budget and what you want.. a decent half system can be had quite cheap which wil keep your cost down compared to a full system if your looking to save a bit of money, a Yamamoto half system which uses the stock downpipes will give a noticeably free-er revving engine, depending on stock jetting, slightly larger jets will probably be needed.

If your happy with the way it is now then just get the stock system repaired, if its in nice condition id probably get it repaired either way when time and money permits as you can always revert back to stock if you feel like it / want to sell and sell the aftermarket separatly.

I have both a stock and aftermarket half system.