If you're happy with the wireless performance, then no need to make any changes.
I suspect with a 12 year old router, you are probably using Wireless 'G'. Best throughput speeds you will see on 'g' is around 20Mbps, on a good day, at the right distance. Add in the repeater, and performance will degrade further in the area of coverage within the extender range, and where the extender range and Belkin range meet.
If you're upgrading, you will get Wireless 'n' or 'ac', as that's all that's available in this day in age. Either will give you a big boost in performance and will likely be compatible with your extender.