With the help of a hex editor, I have figured out a strategy for maximizing a Hunter's critical hit rate. It works as follows:
1. When creating your Hunter, choose Human or Half-Orc as your race. These two races have higher starting Dexterity than other races.
2. Make sure that you roll 15 Dexterity at the start.
3. When you level up your Hunter, reload if you don't get a Dexterity increase. Getting Dexterity early is more important than critical hit rate increase. (Of course, you should stop doing this once your Dexterity is maxed out, and you could stop sooner if you'd rather boost something else, or (particularly in BT3) if you are tired of all the constant reloading at level up time.)

There reason this works is that, as it turns out, your Dexterity affects the rate at which your Critical Hit rate increases. As with HP and SP bonuses from Con and Int, this effect is not retroactive (though that isn't a big deal because there isn't a feasible level cap and XP requirements eventually stop increasing).

A Rogue's thief skills work similarly, but there are a couple things to note:
* Unlike Hunters, Rogues can be Hobbits, which allows them to start with 18 Dexterity; this is a good idea if you want to maximize thief skills.
* Dexterity does not affect item identification; Intelligence, however, does. Therefore, if you want to be better at identifying items, favor Intelligence on character creation and leveling up. (Do, however, note that really high Identifiy skill (>99) provides no additional benefit, and there's the option of reloading or just using Garth's (unless you're playing BT3 with save anywhere disabled and no chapter differences, of course, but even then you could just do your item identification by the Refugee Camp until you learn that one Chronomancer spell).

This method *might* work in the classic games (I haven't tested this), but be aware that, if the version you're playing suffers from the critical hit overflow bug, that the bug will hit you sooner if your critical hit rate grows faster.

Also, don't forget that other stats have their uses; critical hits aren't useful if you can't even *hit* in the first place, and there's still the issue of survival. The only stat that's useless for a Hunter is Intelligence (and Rogues actually have a use for that stat, as mentioned).

Here's another point of advice that, while relevant to all 3 games, is likely most important in Bard's Tale 3:

As I mentioned, you actually have to *hit* with your weapons in order to have a chance of scoring a critical hit, and in BT3, you may find yourself having trouble hitting enemies with ranged weapons. Turns out that the hit chance for them works like spells. This means that:
* Getting a higher Luck stat will increase the hit chance; therefore, you might prefer to prioritize Luck in character creation or leveling up. (Unfortunately, none of the hunter's racial options have good Luck, though other classes that need it for spell accuracy (bards and mages) do have luckier options.)
* Certain items provide a bonus to spell accuracy; these include the Luckshield and the Elf Boots, and in the remaster, they *stack*. Equip both and suddenly your hunter can actually *hit* things (though maybe not consistently if their luck is low). I will need to check whether the LUCK or DIVA spells increase accuracy (I believe DIVA does in classic BT3). If you're playing without the ability to use unequipped items, keep in mind that there's a special quest item in BT3 that can can hit at 70' and is a main-hand weapon, and BT2 has one with 80' range that can be used similarly. BT3 adds at least two more items that provide a spell accuracy boost, but they're not applicable to a Hunter; the Deathhorn (nice for bards, though, and at least in classic versions instant-kills an entire group) and one Rogue-specific weapon IIRC.
* (If you're playing a classic version of BT3, hunters don't get ranged criticals, and I believe the Elf Boots don't have that property (possibly a bug?).)