the lab is totally worth it. You will earn your intial investment and MUCH MUCH more back over the years. I bought mine when I first got my account, back in 2002. My pet now has 500hp and 200 str, and thats with me leaving neopets for a good 3 years. I didn't even use the lab everyday when I did play. If i did, Id assume my pet would have around 2000 hp. Oh boy...
it really all depends on what you value as 'worth it' personally i think its a waste of money...i prefer to codestone train my pets, and if i want to paint my pet a certain color ill use a paint brush, i owned 2 lab rays and never used either