Is it relatively easy to do yourself, or better left to a service tech?

Fortunately, the new tube will have lots more paper on it.
This is of as much relevance to the maintenance of your TV as what the sales guy was saying to you.

Plasmas have no tubes (as in lamps, or even cathode ray tubes..), they require no replacement of anything under normal working conditions. It's like the old style direct view tube TVs. You fit and forget. They fade a little over time and you replace the whole set after how ever many years you are happy to live with it.

The poor guy at the store you bought it from isn't to blame, it's the fault of those who hired him to sell the TV in the first place.

Sleep well tonight, your TV is virually maintenance-free (providing it isn'ta bad apple).

Feel free to check in here before buying your next piece of gear so you'll know what to expect next time.