I've been trying to keep the rank as high as possible at all times; it's a lot riskier, but the payoff is huge, especially against things like the huge stage 4 ships. From what I can tell, the hits multiplier from 1.5 is still in effect, but constantly rather than when you have a full hyper bar, so the extra hits you get from bullet-cancel enemies at maxed rank really add up. Lots of extra stars to nab, too. I die pretty often like this, but it doesn't seem to hurt your chain that much unless you're in a hyper, in which case it breaks (I think).
EOJ: Ah, thanks, interesting. I've been watching some more replays, no-one seems to get Ura midbosses before 1-3 with Bomb or Strong. I guess that's probably just how it is, then... seems like a bit of a bizarre thing to do, though.