That's a fair call as far as personal preference goes, but taking a couple off-specialty Skill Focuses is hardly a significant balance concern. I'm happy with it being cheap; if it fits your playstyle and is a good deal for you, take it!Perhaps not, but it significantly ups your odds of an unreliable one. 1d20+0 will hit a DC 10 check half the time; 1d20+3 makes it closer to two-thirds. I prefer for my character to have at least a chance of contributing in a lot of situations, and just generally seeming like a well-rounded individual, instead of being a one-trick pony who's dumb as a box of rocks (unless being dumb as a box of rocks is a part of his characterization, rather than just a consqeuence of not having any skill points).
You're right that skills can be pumped very easily. Still, for most skillchecks, all that matters is success or failure. Unless you're substituting skillchecks for saves or attack rolls, even having autosuccess on a particular skill you've focused on isn't that big a deal. Again, not something I'm worried about. For most characters in most situations, Skill Focus at half value isn't all that tempting from an optimization perspective. And for those few exceptions, it'll remain worthwhile even if I up the cost a point or two, which is all I'd be doing anyway. I think it's fine where it is.There are many checks for which a masterwork tool doesn't make sense, and others for which it's overpriced (Alchemist's Lab being the obvious example, but even Climb costs 80 gold rather than 50, and that's a big deal for level 1 characters unless the GM is generous). Plus you can stack Skill Focus and the masterwork tool, and ranks and an ability score. Maybe there are other sources of bonuses in books I haven't read, but at least in core Skill Focus has utility for helping your check hit an absurd bonus at the early levels.
It's nice, but you still have the other limitations mentioned: -4 or more to attack rolls is pretty crippling, and 30 range is highly limiting for an archery character. And archers are usually the characters who can most reliably depend on being able to full attack consistently. For a melee character, something like this would be nice... but for an archer, there's a pretty heavy "why" quotient.Being able to full-attack is not something you can rely upon in my experience. And precision damage only matters to a handful of classes. Multiple attacks as a standard action is danged impressive according to everything I've seen (which is admittedly not much compared to professional optimizers, or even people who get to play every week for a year or so; I am sadly not one of those people).