My sister has done workman's compensation insurance and remarked that all the welders were out of work. (or a large number of them). I mentioned that there was a welder shortage in California and she suggested I mention that on some of the forums where they hang out. What I discovered was that there was a number of vocal proponents who argued they wouldn't work in California for the shit rate that was being offered. Instead they would rather be out of work than devalue their time.
So its a fair point, if enough skilled people stay out of the workforce then the economic demand will cause prices to rise to meet the market price. In California its interesting that the tax payers take on that burden and the shortfall threatens the teachers who then jump on to TV ads with their persistent message of non-support.
The question of illegal immigrants came up too but if you look you will find that a skilled welder / carpenter / mason has opportunity in Mexico that they don't need to emigrate for, so its not the issue one might suspect.
You get substitution effects, people substituting unskilled or lightly skilled labor instead. This results in problems later but some of those people will go on to become more skilled which will increase the pool.
A couple of people have mentioned the 'status' question, but from an economic standpoint the pricing of wages should be based on the ability of the population to supply qualified labor not on how 'important' they perceive the job to be. Its not always done that way but it does take personal bias out of the valuation question.
Mike's comment that we need more people in the trades is also tempered by manufacturers who would rather 'fix by replacement' than 'fix by repair' their items. They see someone with a broken washing machine as a motivated buyer, not someone with a problem they can fix. It would be helpful if congress mandated that the information to fix things was made available for free. (think service manuals) While it would burden the manufacturer to write such manuals it would enable repairs and a 'green' industry of keeping equipment running rather than in the dump.
I was hoping that one of the things that would come out of the Auto-melt-down would have been a vehicle that was bare bones, dead simple to repair, and inexpensive. There is demand for such a vehicle but no one is looking to meet it yet.
So "we need more skilled tradesman" as a call to arms has a number of things that it carries with it. I didn't see that the complexity or at least the interconnectivity of it all has been well represented to Congress.