The amount of secondary stats is really minimal unless you are stacking a stat like haste or resilience. Then the amount can be significant.
However, if you are going to stack stats such as Str or Int the losses you incur are tiny compared to what you gain.
For example, on my Shaman (was a 70 in BC I had lying around) which I chardeved in her ele set (so will do my math from that though I am talking mostly about resto) has 28.08% crit chance, 8.94% haste, 15100 hp & 27.91% resilience reduction in a generic pvp set. If I take her to 74 I lose 6.48% crit, 2.27 haste, I GAIN about 1200 health, and lose 6.24% resilience.
Then compare that to the fact that Rshamans scale in a way that makes almost all their heals heal about 25% more at 74 (other healers are about 15-20%). Plus I gain 2 talent points for improved shields which increases earthshield healing by 10% for a total of 35%.
Alone that is enough for me to be of the opinion that the toon would be more powerful at 74 than 70. Thats ignoring the spell resist, improved stealth detection, and increased chance to be missed when attacked by 70's.
(not trying to say everyone is better at 74. Just saying the argument about secondary stats doesn't really hold water)