Yes, yes and yes.
If all you want is to wait for tasking and then wonder why you don't get used more, then don't go to these exercises.
If you want to understand how the Gold and Silver system works and want them to understand SAR capabilities and limitations, ensure that your representative in the Silver/Gold setup has decent comms and can liaise properly with the other emergency services and realise what other capabilities exist among them then perhaps it might not be a bad idea to engage and attend.
At least 80% of UKSAR is overland where the MCA don't have primacy so perhaps that is where more effort needs to be expended by a new and professional SAR service - just putting a coastie with a radio near the Gold/Silver control probably won't be as effective
We have worked with Urban Sar teams, swift water rescue teams, wind farms and the more people who understand what a SAR helo can do the better when the chips are down and there is a major emergency to deal with.