In Felix's thread on the same idea, I gave feedback on essentially the same feats, but I'll address it here as well. I wouldn't allow
Reduce unless its modification was 0 levels because it's too abusable to get something for nothing. Most spells aren't cast at their max range IME so this is not something that is actually being given up to recieve a reduced cost.
As a couple of options to address possible issues is to:
1) Don't allow increasing & decreasing metamagics to be combined. Reasoning: too many possible combinations that allow a beneficial something for virtually nothing in the situation. The examples with fireball are best. Reduced range or singlton & slowen give it to you for practically free & if you use all three, a maximized fireball on BBEG in melee is at same level as original

I will give you the fact that most are only 1 level reductions which aids in the balance of them. (You would have to spend 3 or 4 feats to be able to do this.) But this will address many of the issues people have with them I believe.
2) Don't allow more than one lowering metamagic to be used on any given spell. Again, would allow you to balance them more easily IMO.
3) Don't allow counterintuitive metamagics to be combined. Obviously.
Other than
Reduce, I think
Slowen also is not worthy of an actual reduction & should be 0 level adjustment as well.
To those who are of the opinion that it is just giving spells for cheaper -- It is, but for a cost. After all, these are feats which must be chosen by the character (instead of another feat).
fba827 said:
I haven't read any of this too carefully, but I did have to say what jumped out at me immediately.
You should add a clause
"No spell may be lowered beyond 1st level" - ie you can not make any spell a 0 level spell, 1st level is the lowest you can make anything.
This is an excellent idea that I hadn't come to as yet, but nixes most of the problematic "1st level spells for free".
Geoff Watson said:
How about this: The downgrading Metamagic feats can't reduce the spell level below the original, so they are only useful on spells that have positive Metamagic feats on them.
They are still very abusable, but not as bad.
Actually this makes them just as abusable, especially with quicken spell.