You don't need longer bolts for the real spacers, just the ones you should never use anyway.A lot of people never have problems with spacers, but some people do. There's always the chance that you'll be one of them.
If you get spacers you usually have to get longer bolts which increases the risk of those bolts breaking ESPECIALLY if you plan to go offroad with your X.
Tire rubbing is also a common issue, along with incorrect installation which can cause numerous problems, and there's a few others but I'm blanking.
Because of those reasons I have decided to not get spacers and save my money to get wider tries and rims in the future. Much safer and more reliable option.