Warhammer 1st ed. was the first roleplaying game that mesmerized me. The artwork, the theme, everything… it's a love that has lasted to the present day. I am, by personal history, a first edition player, no doubt.
My first edition book looks like it's been to war - scorched from candles and cigarette burns, tea- and soda-stained, grubby and with a broken back. I think I've GM-ed for 8 years with it in the 90s, once a week. And I still use all my 1st edition stuff from time to time. Certainly the scenarios and source books. I tend to go back to the 1st ed. core rules for the druids and the old faith, as well as the Fimir; The Celtic influences that Graeme Davis put in there. They are part of the Old World, regardless of whether or not the 3rd ed. mentions them.
To me the edition we use to play is almost irrelevant. It's merely the window through which we enter the Old World and that has not changed at all. Warhammer Fantasy Battle has changed the theme bit by bit, but well, that's WFB, not WFRP. The WFRP world is the same that it was in 1987.
The identity of Warhammer lies clearly in the story and the theme and that hasn't changed at all in the 3rd edition. When I prepare an adventure, I need a good plot seed and an interesting setting. It doesn't matter if I use first, second or third edition stats for that and in fact I don't even convert the stats mechanically. I take a rough glance at what makes this NPC special and assemble some quick stats and abilities- the toolkit-character of the third edition makes it very easy.
That said, if you play 1st ed. and it runs smoothly with your group, then stay with it. Never touch a running system. In WFRP, the edition is merely a means to an end.
In fact, you can play all the new campaigns for the same reason. To quote Graeme Davis on the new TEW campaign: "The story is a wfrp story, the plot is a wfrp plot.". You'll find the interview here, the part I mentioned starts at 61:30.
Small but Vicious Special 4 : The Writer Within
You can play the campaign with any wfrp edition, how your players roll their attacks is nearly unimportant.
So you have plenty of equally-minded people here on the 3rd ed. forums. We all love the grim and perilous world of Warhammer and that hasn't changed with the editions.
I'd say, stick with 1st ed. and play some of the new campaigns!