I have a canon EOS 50D with EFS 18-135mm lense. My husband bought me a Canon EF 70-300 mm f/4-5.6 IS USM lense for Christmas. I have no other lenses. Should I keep it or trade it in for a nifty fifty or other lense to compliment my 18-135? I'm wondering if only getting to 300 mm is really worth it...I've been pretty happy with the 18-135 range Thanks.