I imagine that there will be fewer perks unlockable the higher skill you get... and some or even most might require you to pick up lower skill perks to take so you do not gain anything by "saving" them.
That hasn't been confirmed, but that is likely the case. Have a look at the Destruction star pattern. http://nerdtrek.com/wp-content/uploads/2011/03/Skyrim-Screenshot-Magic-Schools.jpg You can see 3 different stars in that pattern. There is the bright yellow star (seen on the bottom one, 2 on the level above on the right, and 1 on the elvel above that in the middle), a dimmer white star (on the second level on the left, and 3rd level on the right), and very dim pink/putple stars (the two top levels, and the nex level dosn on the left).
The yellow ones will be the perks that you have taken (you can see the white connecting lines between them). The white ones are likely perks that are available, but that you don't have. And the purple ones are ones that you currently cannot take because your skill is too low (above the middle line), or you don't have the perk below it (3rd level up on thei right; you don't have the second level so third is off-limits).
Exactly where those skill limits are, we don't know. This also doesn't show if you have to take perks at level up or not. However, there is no real way to "game" the system by holding out. You will still have to take the perks below the top ones first.