I have two L series lenses 24-70 and 14mm and am in need of a longer lense (70-200 or 70-300)my question is since I shoot mostly landscape from a tripod is it worth the expense to go to the L series lense vs 4.5/5 type?
If you're using them for landscape then aperture isn't your concern, but sharpness is. My understanding is that the 70-200's are sharper, but may not be noticeable when stopped down to F/8 or smaller. There are plenty of websites that do sharpness comparisons (the-digital-picture.com comes to mind) so you can evaluate for yourself if you want to drop the money on something you can or can't see.
I think if you're on a budget and don't require top image quality for work purposes then the 70-300 is quite versatile and won't be too shabby when stopped down and on a tripod. I have the 70-300 and it's nice to have the extra 100mm especially noticeable if you're on a crop camera (but I would guess with the two L lenses you have you're on a ff, so the 100mm would be of use).
So if I were you, and I don't need top image quality, I'll get the 70-300 and then invest in some quality variable ND filters, Cokin filters or a time-lapse intervalometer for some extra fun with landscapes.
Here is a good review and comparison with f/4 lens - http://dancarrphotography.com/blog/2010/11/17/canon-70-300-f4-5-6-l-is-review-vs-70-200-f4-l-is/
Check the part where Dan discusses about diffraction issues at different focal lengths.