I personally wouldn't use i ton my first playthrough. It adds its own content and some of it just doesn't feel like Fallout 2. While some of it fits perfectly with the story, most of it was left out for a reason and even with the greatness of the restoration project some parts of the content just don't fit right in or are poorly implemented (gameplay and story wise)
So use the unofficial fan patch or play it vanilla for your very first run and after your first or second playthrough go with the restoration mod.
The reason most of it was left out was because the developers didn't have enough time to implement it all, due to being rushed by their publisher at the time.
The quests added by the RP are, in my opinion anyway, mostly in line with the rest of Fallout 2 - at least in the latest version (2.2). It's apparently in-line with what the original devs wanted, and I think the original devs gave some feedback to the project at some point (although I can't find where that is now). More details here: http://falloutmods.wikia.com/wiki/Killap%27s_Fallout_2_Restoration_Project
Beware that some of the above link may include spoilers if you read too far down the page though!
You also don't need to visit the additional new locations if you don't want to, but since it actually fixes some pretty glaring bugs (over and above the fan-made patch), I recommend it. One of the fixes is that combat works properly (with respect to ammo types), so it's worth it from that standpoint alone, at least in my view.
At the very least, grabbing the fan-made patch is worth it - it doesn't add anything, just fixes MOST bugs (but not as many as the RP).
I forgot to put an 'IMHO' after my opinion ;P
For me at least it was somewhat breaking the immersion at certain points and I liked it more, when some of the things were just left ambiguous. Not saying anything specific, since it involves a lot of spoilers, but anyone who played the restoration project, should know what I am talking about.
I totally and absolutely agree with your point made about the bug-fixing and the ammo, but it just doesn't feel like Fallout 2 to me without a little bug here and there. None of the gamebreaking ones of course....
In the end it just comes down to personal taste, I guess.