Consistency. If you are going to run a subpanel to each room I'd like sub panels, but a mix is not what you want as then nobody is ever sure where to find things. The worst would be a subpanel but some circuits run back to the main anyway - lights is the likely area to see this as those are often shared between several rooms.

If you add a subpanel make sure you can get at it easially to add more in the future. You never know what else you might want in the future. That you think a 30 amp break in the main panel is enough implies that you have a gas stove/oven - you might want to switch to electric in then future for various reasons. Thus make sure there is space for 6 more circuits (2 for the cooktop, 2 for the oven, and 2 for things nobody has thought of today) For the same reason you should get at least 75 amps to that subpanel - even though you will likely only use 30 at max you want that extra space for the future. (I'd go 100 - it doesn't cost that much more and you can upgrade the main panel in the future.

I don't recall NEC saying anything about how much a subpanel needs to feed with, other than "enough". I haven't checked the latest though. Still 30 amps doesn't seem enough for a kitchen even if allowed - some day you will throw a party and that won't be enough for all the things pluged in. NEC requires 2 different 20 amp circuits for counter top use, 15 amps is not allowed, and if I were you I'd consider putting in 3 just to be sure. I'd say less than 50 amps isn't enough for your current uses (and I'd go for 100 on the assumption that the main service gets upgraded some year)

Honestly though, most people don't use subpanels for a kitchen. It doesn't save money and most decorating plans cannot work around a subpanel - this ends up being the big killer.