As an industrial apprentice trained electrician I would say that my own personal experiences tell me what every sector you work in whether it be domestic, commercial or industrial you need to diversify. Although I was trained as an electrician my current role innvolves pneumatics, hydraulics, industrial controls, assisting with production and what ever is required. And why? Because companies do not want to pay for an Electrician and fitter or other skills that are required.
My point being the domestic and plumbing sectors have been attacked due to advocating competency via short courses and admission to self cert schemes. But maybe at the domestic end of the market they are potentially adding value to the customer. Lets face it if a tiler can be made competent to install sockets in a kitchen let the one man or team complete the job. But I hasten to add that if a domestic spark is any good and does a tidy job he should already have at least basic plastering and maybe tiling and concreting skills. He should with minimal training(maybe a short course) be able to attain a decent level of skill in these areas.
I generally do my own tiling but when I've had builders or tilers in and they do a good job and work hard I think they are worth at least the same as sparks due tio the effect they have on the job. However when on various electrical industrial jobs sparks should be getting over and above that of tilers and builders. This is because these sparks are beginning to utilise there technical knowledge more to complete their tasks.
Anyway, for what its worth grab as much money as you can!
Cheers
Working Around Other Trades !!! 
