I've always had a small worry about this same scenario. In my opinion, who knows what cockeye renewal loops registrars are going to make us jump through 5 years from now. That is why for my main domains I always keep them renewed as far out as possible, which is 10 years for most.
I figure I can afford it today, what if I can't in 5 years? Buys me some extra years at today's discounted prices.
My only advice, don't do this all your domains. Just the ones you have built sustainable sites on.
It also doesn't hurt from the perception of stability. If someone sees your site is registered until 2019, and a competitor is set to expire next year, they may choose your shop because of the perception that you will be around for years to come.