I prefer downlocking reel seats with either a cigar grip or a half-wells (Fenwick) grip. However, I see most production rods have uplocking reel seats and reverse half-wells grips. Does an uplocking reel seat have some advantage I don't know about, or is it simply a matter of esthetics?
This isn't a question of earth shking importance, but I am curious, so any information will be appreciated.

It's really just a matter of aesthetics. Most commercially made fly rods in the light to mid line weight categories utilize reverse half wells grips which mate well to uplocking seats. The hooded cork is favored by fly fishermen and the makers respond by giving them what they want.

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The advantage of an uplocking seat for bass fisherman allows the removal of a foregrip and placement of a finger on the blank for that cursed word that starts with an "S". The shortest end of a spin seat is the slotted end and this allows the seat to be set up for more finger contact with blank. If you hold the reel post between the ring and little finger it then becomes quite easty to extend the forefinger to touch the blank. This technique is extremely important for drop shot and shaky head for those using spinning rods. This is a logical extension Rich Forhans concept of the exposed blank seat.

There is an additional advantage to the uplocking seat, in that it moves the reel up slightly, so that if one stands their rod on the ground, the reel is not as likely to get exposed to the dirt.

With a heavy reel, the rod is easier to cast with the reel as close to your hand as possible. I like the downlocking seats on light rods, but must admit that I cast by holding the reel seat in front of the reel with my hand jammed back against the reel. To me the uplocking seat cheats you out of a couple of inches of length on short rods.

Thanks, I thought as much. I'll keep building rods to my preferences then.

Bill Stevens has it correct, in my opinion. For an added nice touch on a rod that you want to contact with your finger, as in jigging/drop shot/etc , do a conical epoxy ramp from the front of the reel seat to the blank. It really is comfortable, sensitive, allows a place for a feather inlay if you choose to do one, and the shape is more pleasing to the eye than just an abruptly ending reel seat. I've experimented with a lot of shapes for the ramp and found a simple conical taper to be the most comfortable.

Also, don't forget to cut off the reel seat to a length that just allows clearance to attach your reel. You don't need that extra 1/2-3/4 inch of threads.