Certainly, MRBO has a substantial affect on the code generated by the jitter. Any access to a field of the class results in a call to a helper method implemented in the CLR instead of a single CPU instruction that accesses the field.
This is inevitable, only the CLR knows whether the object is actually a proxy or the real deal. And a proxy needs to emulate a field with a remoting call. If it is not a proxy then you still pay for the helper call overhead, an easy order of magnitude slower.
Whether that truly has an impact on your code is impossible to predict, we're talking about nanoseconds here. You only do something about it if the slowdown becomes noticeable.