Dying Router?

How can one ascertain if a router is beginning to 'die'? I have a Time Capsule (1TB; 3rd gen) which I've owned for 3 years now. Before, when doing speed tests I would consistently get the speed I was paying for, but lately it's become more erratic. I have FiOS, so I don't think there should be problem with the speed consistency (I maybe wrong).

I downloaded iStumbler and noticed that when I'm downstairs, I get about a 50-59% signal strength and when I'm upstairs (literally next to the router), I get about 70%. My place isn't big, it's just "tall" (high ceilings) and it's a loft. So, my MBP isn't really that far away. I also switched to Channel 7 since it seems to be the only one that wasn't used by nearby WiFis.

I've been eyeing the new TC (2TB), so I may just be trying to justify the purchase and imagining things. Haha. My MBP isn't 802.11ac capable and none of my other devices are either. I'm just thinking that with the newer hardware, the signal strength would be much stronger. I have an APE that I set up to extend network, but it makes no difference in signal strength.