Well, as someone new to this who spent 2 months researching...I'll throw in my 14 cents :^)
First, I read every message board and post on the subject I could. I had ordered a 2002 300 mxc and wanted to buy all the parts before it got here. I knew I wanted at least a top clamp as I like the cycra clamp mounted handguards and ya can't do that with the stock setup. I saw alot of "best thing since sliced bread", "really only need it on the bigger 4 - strokes", and "all you need is properly setup suspension". I went to Emig and read what they have to say..heck, they even sell a 22 mm offset....
Then, I spoke to someone I know that is a professional suspension god (did miracles for my 91 cr 250) and many times over KTM owner. Basically, he said with proper setup, and the knowledge that the ktm's won't quite turn like the other 250's where they like to square off the turn and shoot out, ktm's carry more corner speed.
Well, since most of my riding is medium to slower and alot of very tight squirrel trails, I was a bit skeptical, but I trusted him. I got the bike and rode it straight for 4 hours with nothing more than adjusting the rear preload. Now, I'm wondering if I'll even need the Wer damper I have ready to bolt up. It is slightly slower than my cr, but much, much more stable. I was railing around a friend on an 02 cr on flat fire roads, and it definately wasn't the limiting factor on tight trails. If I noticed any difference in handling between the bikes I was looking at getting and rode (crf, cr, yz, yzf) it was how stable the ktm was. Slow steering was never an issue.
So, now that the motor has a couple hours on it and the suspension is slightly worked in, they are going in today for revalve, rework, revamp..whatever, to get them perfect.
I think the people are right that said properly setup suspension solves the slow steering.
Now, if you want really quick steering, there's nothing wrong with getting the 18's, but I don't consider them a necessity. I've got the first enduro of the season in 2 weeks and I'm totally confident the KTM will handle perfectly.
good luck, have fun, be a kid :-)