How to upgrade my Rega Planet based system

My suggestion is to work on power, power conditioning and/or power cords. The Mira is small enough that you can run it through a conditioner without current limiting becoming a problem. In my experience, dedicated lines is the highest return on investment, followed by a conditioner, and then cords. This will improve bass, expand the soundstage and improve detail, without changing the basic character of a system that you are happy with. There are many good choices; My bedroom system is a Linn Majik on a 20A circuit dedicated to the system, a Tice Solo ($400) and a Cardas cord ($185?), and it makes terrific bass through 6.5 inch ported woofers. You can get major results for less than $1,000.

I would like to second the recommendation for a sub in your system. I once had the Rega Planet and Mira with Jura speakers. For a time, there an REL Storm II in the system, and it helped bass extension greatly. It was easy to integrate and was very "musical." By the way, The Rega Vulcan is made by REL. You could prpobably find a good used REL Strata or Storm for about the same price as a new Vulcan. Used Vulcans don't turn up very often. Either REL unit will be more powerful and will go deeper than the 8" Vulcan. In my exporience, the Rega gear will benefit from power cord upgrades. The stock ones are as cheap as any I've seen. I wouldn't go overboard on the power cords though.

I third the recommendation for a sub. A REL, Rega (which is designed and made by REL for Rega), or ACI sub would be the first choices.

If you like the upper octaves of your system why risk changing them ? Also these subs will take you down to 20Hz and give real bass-drum kick. I would bet you'd be looking at a lot of money to upgrade your amp and speakers to achieve the same.

All of the above; a subwoofer, power cables, and conditioning.

Buy REALLY expensive power cords. Like Siltech Compass Lake. Your dealer will be glad you did.