[chris_i30gd]

According to a net search in google I found that silentblocks should be changed every 70.000-100.000km
and they are related to the road noise, comfort or hanlding. Have you ever checked or change silentblocks?

Are there better silent blocks than oem  that give better comfort and less road noise in our  i30?

[Asterix]

Had to google silent blocks. 
I guess you mean all the bushings in the suspension in general..? It would most likely be beneficial for the ride comfort to have them changed at that interval, but in my 10 years as a service manager I've never had a costumer ask for them to be replaced if not defect.

I'm @ 287.000 km on the stock bushings...   

[tw2005]

In my  opinion it's not just distance but in time these will deteriorate. For the FD in the front arms, the small rear bush tends to tear and separate.  If you can get new arms cheaply I'd go that way if it had to be done. I've had a vehicle with 170000K and 377000K with these gone yet my 200000k hatch was fine, I replaced them anyway. I'd only replace them f they had failed.