HTC Radar 4G - Time to upgrade

Hey Tribe,

I've been using Windows Phone since it first came out. My first device was Samsung Omnia 7. I gave it to my brother a couple of years ago and switched to HTC Radar.

To my surprise, my brother's Omnia 7 and my Radar still work perfectly smooth, and they have all necessary features like Facebook, Twitter, Email, Internet Explorer and a 5 mpx camera which I must say that it is good enough for "social" photography.

Now, after so many new lumia devices being announced each year, and a later WP 8.1 with Cortana, I am thinking to upgrade to a newer model with which I can use latest OS version.

My question is: Do all these technical specs (like CPU Mhz, RAM etc..) really make any difference for an average user?

I'm asking that, because if I compare my aged Omnia 7, HTC Radar with some new lumias, the OS interface works almost similarly smooth. The only reason I want to upgrade is Cortana and some new OS features. And I think if my HTC Radar was compatible with a newest WP 8.1, I wouldn't even think of upgrading..

Strange situation, isn't it... :)