having your partner on the same system does have a small advantage but unless you duplicate lenses you end up having difficulties sharing and if you do duplicate lenses then it doesn't really matter what system you have duplicated it on.
For ample, lets say you buy a 100-400 and you go to S.A. for a safari, well only one of you has the ideal lens so how are you going to share this?
If you both like different types of photography then it can work out because you will use different lenses, but then the same kind of argument holds that if you are going to use different lenses then putting them on different camera systems doesn't change the equation.
The advantage is more subtle, things like sharing the same batteries and charger or being able to swap cameras and have the controls feel right, getting photos that have the same skin tones and rendition etc..
One thing to be aware of the Canon 65mm is that at that focal length it isn't ideal for live insects. Something like 105mm works better on a crop, or even the 150mm Sigma. You get more working distance, lighting is easier, less likely to scare the insects etc. Also the Canon 65mm cost similar to a lens like the 300mm F/4.0 which is good for wildlife. If you are on a budget then I would look at the Tamron 90mm, Sigma 105mm Macro lenses, available for both Canon and Nikon.
Now I am not trying to persuade you to go Nikon, although the D7100 is undoubtedly a much better camera in itself, just trying to let you know some additional info in regards to macro lenses etc.
My Wife has a Nikon D7000 but we never really share lenses, she like her 18-105 kit lens and I gave her my 50mm f/1.8 I never use, we have never shared lenses since then. The only reason she got the Nikon was again, the D7000 was just the best crop camera you could buy at the time.
