A few points:
1 - The Canon 70-200f4 is a real "bargain" in L lens terms, and every bit as sharp as the f2.8 LIS
. I've owned them both - f2.8 and IS
is important for the low light work I do, but for aviation, the f4 is just fine.
2 - The D60, so presumably the 10D as well is capable of showing the difference between Canon L glass and Canon consumer lenses. No, L glass won't make you a better photographer - but it will help you make the most of any situation.
3 - the 80/20 rule applies to L glass. You'll pay an 80% premium for a 20% improvement in quality, moreover, that improvement will probably be a significant factor in only a small percentage of your shots.
4 - If budget is a significant factor, and you are not "Canon bound" you should give consideration to the new Pentax (good range of quality lenses at sensible prices). Also, there is a fair probability that Canon will be releasing a more affordable 4mp DSLR late summer, which would be a better match to consumer Canon lenses. Finally, if very large prints are not your aim, the D60/10D 6mp and ultra sharp lenses may not be necessary - used D30 prices are in freefall, and image quality is every bit as good as the D60 up to a certain image size.
Colin K. Work, Pixstel