all of this IMHO:
I don't think sFoster is right about grabbing. Your match may not contain as much grabbing as he'd like, but plan 9 doesn't really give you many opportunities to grab. Unless the opportunities sFoster refers to is combined with his other suggestion: pivoting and using a move rather than hitting both sides. You could grab plan 9 after a shielded aerial lands behind you if you pivoted, i guess. I never do that against Wario, but maybe i'm a noob.
sFoster is definitely correct about you needing more down tilt. Down tilt can rack you lots of damge against Wario. Even with good DI, i think downtilt downtilt Fsmash can be unavoidable.
Sometimes against Wario, i just stand still and decide I'm either going to shield grab or dtilt his next approach, because i know that i need to get downtilt in the game somewhere. And it works, it there's landing lag i can dtilt out of shield, if there's not i can grab. (of course his approach sometimes succeeds entirely, because the plan is imperfect)
I don't (the benefit) understand or recommend sFoster's Din's fire toss approach. If you jump and toss Din's fire with you, it will be airdodged. Then he'll have to finish the airdodge, and you have to do the landing animation for a helpless faller (you used Din's in the air, it counts as a recovery move). I don't see how that really gives you much advantage. The general idea of the approach is just to do something on your terms, which is accomplished, but against Wario i don't think it's a good idea to sacrifice the ability to sit back, think, and just try to react.