So recently I picked up a set of Enkei RPF1's (15x8) for next to nothing and I couldn't be happier. They're wrapped in 205/55/R15 and my prior set was 205/50/R15 (weird I know). See the picture attached for quick look

= Car Background =
Bought the car around a year ago from an older fellow who appeared to love the car well and truly. With the car he gave me spare shocks and springs but no full sets of 4. At the moment it's sitting on king springs - no idea as to the length or rate - on all 4 corners with bilstein shocks up the rear and KYB AGX shocks up front. He DID track it occasionally although in his own words, he wasn't that great at it so he didn't beat it's head against a wall. Regardless, the shocks and springs no doubt have definitely seen some distance and time. I'd guesstimate a minimum of 4 years on each shock and spring. I daily drive the car and I've never taken it to the track myself although I would like to eventually on the odd occasion and I've definitely come to enjoy doing the mountain runs with the current stiff suspension. So I'm not overly fussed about the ride being 'a little harsh for a DD'.
= Questions, Queries, Problems and more of my nonsense =
(I'll list them in order of logic and reasoning)
1. The rear shock is leaking so I need to replace it. Do I buy 1 Bilstein shock? Do I buy a set of 2 for the rear? Do I buy a complete set of 4 or do I just throw it all out and get the whole shebang and buy a coilover set? I have no idea! I figure I can justify the upgrade because I can raise/lower the front/rear and thereby stop the rubbing although at the same time I'm obviously a human and want to keep funds in mind. Budget vs effectiveness, thats my question here, whats the best decision?
2. From what I understand my current setup is not exactly poor or 'budget', moreso just old and worn. Is my current setup with Bilstein/KYB Shocks and King springs superior or inferior in terms of straight purchase value to a coilover like the TEIN Flex Z? In other words, am I actually downgrading by switching over to coilovers regardless of the age of my current system?
3. And finally, the question of the hour! If coilovers ARE a good idea, is the TEIN Flex Z a good choice? I've found them here a hell of a lot cheaper than some of the higher spec coilovers: https://www.rhdjapan.com/tein-flex-z-co ... -nb8c.html
Here's the others I've looked at with rough pricing after shipping:
TEIN Street Basis Z ($700-800) - everyone says they're the budget option you'll regret. No adjustability and manufactured in China.
TEIN Street Advance Z ($900-1200) - similar to the Basis although with damper adjustability and still made in China. Mixed reviews on this one.
Megan Racing ($750-950) - Supposedly there's better options for the money your spending (like the BC or TEIN) and alot of people have complained about build quality.
Yellowspeed ($1250) - Apparently used by alot of mx5 track enthusiasts. Again though, some people bag them to the days.
V-Maxx (???) - I know next to nothing
BC Racing ($1400-1600) - And I know next to nothing again.
Either way, I know it's a big ass thread that I've left here so I apologize for the lengthy read, I just really need some help and advice here. What do you think I should do? Am I being dumb? Should I just replace the shock? Should I buy the TEIN Flex Z? Should I just roll my guards and raise it up to stop the rubbing? Any advice on anything at all would be appreciated on my behalf at this point!
Thanking you all in advance! Your all awesome!