Gerry Conway really seemed to raise his game with George onboard.

Greg, with JLA I think it was probably more a case of a great artist making the stories seem better, rather than Conway raising his game.  In particular, the first two JLA issues George drew were parts 2 and 3 of a story written for Dick Dillin to draw.  Dillin had completed the first 2.5 pages of issue #184 and then passed away unexpectedly and the assignment was handed to Perez (who redrew Dillin's pages and then finished the issue).  So for at least those first two issues, Conway had no idea Perez was going to be the artist when he wrote his scripts.  And given that there were musical artists during the span of issues 184-200 (with Buckler, Heck, and Perez all doing issues) it's possible Conway didn't know who was going to be the artist of any given issue when he wrote.

Here's a fun contrast... Dillin's unpublished splash page for JLA #184, and Perez's published version:

 

Here's one more... page three, which Dillin had 2/3 completed when he passed away, and the relevant portion of Perez's redrawn version:

The Dillin pencils come from Twomorrows Publishing's Alter-Ego Magazine #30.

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And that's what I admired about him the most.

I will say something somewhat sacrilegious - I do not at all see the appeal of his 70's - early 80's work. This JLA page above was published around the same time as X-MEN#137 - and to me it's a night and day difference of quality and skillmanship.

BUT - George himself had said in later interviews that he was completely self-taught, and dogged his own work as I am doing here. He could have rested on his laurels and fanbase, but he expressly strove to get better and learn the proper fundamentals. And boy did he.

Maybe in retrospect, but when I was buying in the seventies there were barely a handful of artists that really had me craving for more, and a young George Perez was one of them. 

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I cannot agree more. George's first Avengers run was the start of my comic collecting.