I actually use that double grenade thing quite often, usually at mid to long range. Often people will see the first grenade coming at them and stay just out of its range, but then you huck a second, fresh nade near it right as it blows up, doubling its range and catching them off guard. You can increase the range to the top, sides, or even under the first nade (if it's on a platform or still bouncing or something). People don't usually see it coming either. I would say its a trick/timing worth learning and applying where you can.
Bonds, I won't be making it to the CO tourney, sadly. No one could drive. Good luck. I will be attending a local tourney though.
For the past few local tourneys I've been doing this weird thing where I'll pick a random character or two 1-3 weeks before, practice with them a bit, then see how far I can get with them. I got third at the last tourney going all peach and DK lol. I'm going marth and ICs this Saturday, we'll see if I feel the need to pull my snake out against someone.