About the best advice I could give as well...Spent A M M O is your friend...when it comes to accuracy !I also have a 27, great gun! If I were you, I'd take the money that you're going to spend on upgrades, and use it on ammunition instead. Nothing will do more to increase your accuracy than lots of ammo.
That's cool...night sights are helpful, for sure.I also have to agree. I own a G27 as well and its completely stock. Spend the money on ammo and practice often.
I thought that i needed a ligher trigger in order to shoot it a little better, but a friend of mine picked it up and showed me how accurate of a gun it is stock. Since then ive trained a lot more with it. Ammo really is the best 'upgrade' you can buy.
With all that said, i will get night sights on it someday....