I like the idea, but I don't think I'd put it in my game. The current batch of metamagics balance an added effect with a spell-slot penalty. These proposed metamagics attempt to balance a spell-slot bonus with an effect penalty.
The problem for me is that in a lot of cases, the effect penalty isn't a penalty at all. Singleton Spell, for instance. As a player, my party very, very rarely goes up against hordes of underpowered critters. Instead, we often fight a single Big Nasty or a Nasty Trio. As combat swings into gear, I'd love to be able to drop a Fireball on the Big Nasty/ies, but getting my allies in the blast foils it.
Enter Singleton Spell, making my 3rd-level attack spells not only do a lot of damage dice, but allowing them to hit my enemy without any fear of catching my allies as well. As an added bonus, they'd only be 2nd-level spells.
Buffing Spells are supercharged thanks to Slow Spell, which would allow me to spend more time casting them (meaningless in camp,) in exchange for -1 spell slots. (Or was it 2?)
It's a nice idea, but I don't think it works. With the current metamagic, the drawbacks are always drawbacks, even if the benefit fails to materialize (such as a Silent Dimension Door.) But with these, there's a good chance that even the drawbacks might work for you, and that doesn't sit right with me.
