I am nearly ready to launch my renovated 17. The work including adding a jib, so the boat went from an SE to a Sport. However if you are concerned about staying class legal you should take some care about how you do the conversion.
Hobie sell a conversion kit, then you get a jib. I tried to buy bits and pieces, and whilst that got me over the line in the end, it would have been better if I just paid the money in the first place.
I prefer a jib, it does add power, and if you have a passenger that helps. It will also help with tacking.
Whether it's a good idea depends on you and what you want, and perhaps the sort of winds that are typical of your area. In this forum there are some really experienced 17 sailors who might offer some words to help here