Modern keyhole cockpits are often around 33 to 36 inches long. 30 inches is considered fairly petite. If you are going 30 inches you have little of the advantage of a long cockpit, and none of the advantages of a smaller one IMO.

I agree (in part): for me, a cockpit with an opening shorter than 32" is usually not workable.
I'm 5'10" with a trouser inseam of about 30".
Paddlers with different leg lengths, different flexibility, etc. will prefer different cockpit sizes.

The seat position relative to the cockpit opening is a big factor as well- both in allowing feet to get under the deck when sitting, and also allowing the paddler to lean back if doing a layback roll.
An acquaintance bought a glass Wilderness Experience boat and neither of us could get our feet inside unless we were siting on top of the aft deck. The seat was located quite far from the back of the cockpit.

Comfort while paddling is my prime consideration, so my seat and footrests are tweaked and reworked until I am really comfortable with the arrangement, which differs in every boat.

This implies that a 32" cockpit can't be comfortable. For me, a cockpit that doesn't allow me to 'put my knees up in the middle' when paddling in calmer conditions would be totally unacceptable. To each his own, as they say....
;-)

Apart from that, I don't put much consideration into entering and leaving the boat, since I spend very little of my kayaking time doing that.

That's fine, since you are an expert and experienced paddler. However, it's no joke trying to get a beginner back into their boat if they can't get their legs into the cockpit and then twist upright (in a standard assisted rescue aka T-rescue). And a lot of people have trouble sitting on the back deck and sliding their legs into (or out of) the boat without losing their balance - it's an ideal way to start the day badly for a non-expert. (Even worse is the beginner snapping their paddle using it for support...)

Recommending 'ocean' cockpits to non-expert paddlers (who know what they are getting into) is not something I'd ever do.
Aside from folks paddling 'rolling boats' like SOF 'skin' boats or the Tahe Greenland or the Black Pearl, I never see small cockpits in my area. I'd say that less than 5% of paddlers in my local club (300 members) choose smaller cockpits. This also means that small cockpit boats are an extremely hard sell, aside from the rolling boat set.

Changing the cockpit size on some designs is not straightforward - Bjorn Thomasson has pointed out that the inclination of the cockpit rim affects accessibility. So, if possible, it's a good idea to pick a plan with a 'standard' 32-33" cockpit, in my opinion.

and the deck, which is my work surface while I am at sea, closer to me. Map reading, compass reading, reaching for my dark glasses or a water bottle, stowing my hat under a deck bungie... All these little things become so much easier with a shorter cockpit.

Agreed- it's a long reach up to the chart on a boat with a standard cockpit. I have my GPS on an 'arm' so I can put it 'in my lap'. Also, a spare paddle on the foredeck is out of reach for a lot of folks, with a standard cockpit.

I know that entering bum first and exiting feet first in a shore break is very handy, but how often does one do actually do this?

Every time I paddle....even without waves, it's just a lot easier.

But everyone likes a tight fit

I don't want to be falling out of the boat or slopping around but I don't like a 'tight fit' because it interferes with an efficient forward stroke. Most of the 'ace' Greenland roll folks seem to like a tight fit over the legs but some side-to-side movement.
So there's no rule on fit.....