Do I have to get a new camera to take advantage of a higher end lens?
I have a Sony A300 which at 10 MP is fine as I don't enlarge to more than about 22x15cm usually. A lot of what I shoot is in manual mode. What I am getting at is that I don't have much need for the fancy metering and high MP count of the higher end cameras although this may just be my ignorance about them. However, my usual lens is an old Minolta 35-70 (£50 from ebay) and this has limitations. I popped into a Sony store one day to have a look at a 16-80 for about £500 and a Vario Sonnar for about £1200. The salesperson was reluctant to humour me in these choices and encouraged me to buy something like an A65 otherwise I would not get the full benefit of an expensive lens. I understand that they obviously want to push their latest cameras but is there much truth in the idea that you have to have a fancy new body to take advantage of a more high quality lens? I am looking for this zoom range and the reasons for getting a better lens are: better clarity, reduced spherical and chromatic aberration, reduced lens flare and speed of focus.
I believe this principle should be the same for all makes - not just Sony so I am not looking for advice only from Sony users.
Thank you for your expert advice.