I do not think that minority languages should be preserved in a country where it isn't the national language. Preserve it in your own country sure, but not where it will be seen to be divisive.
I'm not sure that you can successfully artificially preserve a living language. The need for humans and communities to communicate with each other will always trump a sense of tradition or identity. The only way to encourage the use of something that has limited practical value is discriminate against the natural favorite, or just offer some reward. Nectar points, for example, encourage you to pay a higher price at Sainsbury's for the same product available for less at ASDA. In the case of protecting Welsh, this has to be done with tax-payer's money as there is no investment value for the private sector, this makes it unsustainable in the long term. As the recession deepens and you're looking for cuts...
Preserving a language is doubly impractical because by preserving it, you define its boundaries. You can't preserve it, and let it evolve in the way living languages do. What's welsh for i-phone, or digibox, or tweet? English language acquires new words and drops old ones continuously, in a thousand years you might not recognise it as the same language.
Thats not to say it should be left to vanish.