yes the gold coaches are the way to go. Not only do they "boost" some of your attributes like forehand, bh, serve, etc. (between +5 and +15!) but they also give you special skills like better return, more precise serve, enhanced topspin or slice (for you

). Actually i think its a very good idea so we can really mold our player and change coaches to fine tune to our liking.
The only downside for now is that the coaches you unlock are only unlocked for a specific created character. I made different type of characters and the gold coaches i was looking for didnt appear in my list... maybe there's another way but i don't know it yet.
Also don't forget that to be able to get the special skills and attributes from a coach you have to do their objectives (could be: make 60 winners, 90 slices, etc.)