It has the advantage of never running out of blasts, since (for most classes) meta-magically enhanced cantrips and orisons cast out of higher level spell slots don't expend the spell slot when cast.This is only true if the metamagically enhanced cantrip would still be 0 level. If a cantrip is enhanced with metamagic to a higher spell slot, that spell level slot is still consumed as normal...
A cantrip is only not consumed if you cast it as a cantrip, at 0 level. If you enhance it with metamagic, it is a spell of whatever level the metamagic turns it into. Those higher spell levels are limited and consumed upon casting.
Unless you are privy to some errata, this is not how I read the rules. Metamagic feats (except for Heighten Spell) do not change a spell to "a spell of whatever level the metamagic turns it into". Instead they
In all ways, a metamagic spell operates at its original spell level, even though it is prepared and cast using a higher-level spell slot. Saving throw modifications are not changed unless stated otherwise in the feat description.
All of these metamagically enhanced spells still operate as 0-level spells, but require that you have a higher level spell slot to cast them. If you don't have a higher level spell slot you can't cast them, but, if you do, casting them doesn't consume the spell slot. This is because the rules for consuming spell slots are written in terms of the spell's level, not in terms of the level of the spell slot.
Wizards can prepare a number of cantrips, or 0-level spells, each day, as noted on Table: Wizard under “Spells per Day.” These spells are cast like any other spell, but they are not expended when cast and may be used again. A wizard can prepare a cantrip from an opposition school, but it uses up two of his available slots (see below).
Oracles learn a number of orisons, or 0-level spells, as noted on Table: Oracle Spells Known under “Spells Known.” These spells are cast like any other spell, but they do not consume any slots and may be used again.
Arcanists can prepare a number of cantrips, or 0-level spells, each day as noted on Table: Arcanist Spells Prepared. These spells are cast like any other spell, but they do not consume spell slots. As with her other spells, these spells are not expended when cast.
Cantrips can be cast again not because they use a 0-level spell slot but because they are 0-level spells. Metamagically enhancing them doesn't change them into first or higher level spells, so the special rules for 0-level spells still apply. For prepared spell casters, they are not consumed when cast. For spontaneous spell casters the spell slot is not consumed when a 0-level spell is cast from it.
Some classes call out cantrips or orisons to be treated differently. For example the Inquisitor (published in the same book as the Oracle) has the following text instead.
Inquisitors learn a number of orisons, or 0-level spells, as noted on Table: Inquisitor Spells Known. These spells are cast like any other spell, but they are not expended when cast and may be used again. Orisons prepared using other spell slots, such as those due to metamagic feats, are expended normally.