For normal proficiencies, if you're dealing out +'s for weapon proficiency, you're also going to have to give the monsters +'s for their attacks.
A +1 can make a big difference between hitting and missing, especially in the older versions of D&D.
By the Book (tm), proficiency means you dont get penalties, not that you get a bonus.
Though, if you're playing classic D&D, and not using the weapon mastery rules, I've often allowed fighters to pick a favourite weapon, that gives them +1
Depending on your ruleset, weapon specialization or something similar could get you a bonus.
Gary frowns upon many things, such as removing demihuman level limits, AD&D variants that allow the player to customize his character (outside 3E) or even helping out 1st level characters to survive.
However, the fact of the matter is that agreeing with him or "his vision" of the game has never been a requirement to play it, and he has been extremely vocal about this. There are rules, DM'ing techniques, editions, house rules and general gaming ideas he disagrees with, but trust me when I say I know from experience that he won't fault you or reprimand you for disagreeing with him. As a matter of fact, I think he enjoys the dabate and how different people percieve the rules--as long as you keep it civil or are not trying to sell him 3E, that is. :D
He has always advocated that people play the game however they feel most comfortable with and however makes the most sense for their campaign, not according to something he said because it came "from on high".
If you want, you can talk to him about this, actually. There's some boards around that he visits every now and then under the guise of Col_Pladoh and he rarely leaves fan mail unanswered. Just a few pointers, don't ask him about Greyhawk, what his plans for 2ed were or what he would change in 3E. Basically, anything post 2ed/WotC era (pretty much all AD&D after Lorraine Williams took TSR away from him for good). Understandably, he declines to answer those questions for personal, moral and slightly legal reasons, so he rarely ever comments on them. He also has a strong policy of not discussing his PC's (Mordenkainen, et. all) or those of his players. ;)
A +1 to hit typically doesn't make a huge difference. If your damage is 1d8+2 & you get 3/2 attacks per round, a +1 to hit will increase the average damage you deal per round by 0.4875 hits.
A +1 to damage would have a bigger effect.
I think it's cool to give PC's limited +5%s to make them unique in certain ways. Although I not above making them spend some XP or take some kind of penalty to offset it.