Yes, we won't know whether coe will shoot up again to sky high figures again. If end next year close to 100K then it will be even tougher for me to renew.
So to say, you feel it is low now?
Gosh that is why the demamd is still pretty strong now, well...
Beside that point as many mentioned, many will drive til the 10th year and see how, not only on the COE then but how your car's condition will be and is there a better car(brand new or pre-owned) out there worth for your consideration to really decide to buy another car and scrap your current or just to renew it.
At the end of the day, just trying to stretch the dollar to make any purchase more worthy.
But beside that, if you feel it is a good time and price to renew, go ahead.
Guess your current ride was bought at 2008 when COE was pretty low hence rebate is low. If to forgo your parf earlier seem fine too(since you plan to renew; thou your dep calculate to be slightly higher);
JUST DO IT.
As nobody now can tell you what will 2018's COE price be.