The difference is in the details.
If you are holding a canal street rep next to a gen and cant tell the difference - then you really should not be buying the 300+ models as it would literally be throwing your money away. And i do not mean that as an insult in any way. There are a plethora of members who scrutinize every detail of a watch in comparison to the genuine. Lug Spacing, AR, Crown guard widths, bezel numbers, bezel pearl, second hand sweeping motion, material of the case, and this is to just name a few.
With so many members modding their watches or getting a TC submariner and adding gen parts, there must be a reason for this right? Its because the basic rep just does not hold up to par with the genuine. (As far as we are concerned) but If you are happy with your canal street rep, wear it and save your money.
Once you hand out here for a while, and start reading all of the reviews that members right comparing the smallest little detail, you might see that yours now needs an upgrade, or you might still feel like yours is just fine. At the end of the day, its just a matter of preference.
If you need a head start, post a picture of your watch and the Rolex gurus will let you know what is wrong or inaccurate.