I have a huge soft spot for TVR having owned a 4.0, a 4.5 and two 5.0 Chimaeras. My conclusion is that the 5.0 is the one to have IMHO.
By todays standards even the 5 is not particularly powerful, they are not particularly well balanced in the handling department and they are certainly not that well screwed together. However, all that low down torque and light weight make them hugely entertaining to drive.....and the sound....
Running costs in my ownership of the above 4 Chimaeras was modest. No big issues experienced at all. Pretty simple beasts really. Biggest issue now is a rusty chassis. Thing is, the light weight, instant torque, coupled with the comedy handling and lack of ANY safety equipment made them such a massively entertaining and exhilarating experience. Simply not allowed to make cars like this any more and its quite hard to find anything similar.
I also had a Cerbera 4.5 for a couple of years. Still miss it to this day, but that one cost me quite a bit to run and nothing particularly big went wrong with it! One of the quickest cars I have ever owned to date and such a sense of occasion to own and drive. I would have another one in a heartbeat! I wouldn't be so interested in owning anything with the speed six lump though. I understand that its a very characterful engine, and they can be made good, but a rebuild is to be fully expected if it hasn't already been done by one of the reputable places.
All of the above have been pampered weekend cars. Whilst you certainly could, I wouldn't recommend TVR for anything else.
As for viable replacements, I went on a bit of a long mission to find an alternative that met similar criteria for me. Few interesting twists and turns along the way with a pair of modified Mitsubishi EVO FQs running big power which where incredible from a raw performance, drive and reliability perspective, but left me cold on the aesthetics and general sense of occasion. Also 4.5k service interval was a but of a pain.
Next up was an Aston V8 Vantage manual, followed by a Vantage sportshift roadster. Superb cars. a little more costly to look after but both very reliable overall. Huge sense of occasion but with only just enough performance to keep me happy. Performance is actually there, but they feel so mild and docile until you get right up into the high rpms. (I had 4.3 variants, 4.7 would go some way to fix this, V12 would certainly but they are over budget still!)
For the Aston, whatever model you look at I would say go for a manual. Whilst the roadster was fun, the sportshift transmission was a let down and I by far preferred the manual. Both felt really special, beautifully put together and held their money very well.
Next up was a C63 AMG coupe with the performance pack. The 6.2 V8 engine in this car (and many other Merc variants) is an absolute masterpiece! Mine was just shy of 500 hp and I loved it for the fairly short time of ownership. I would describe it as a muscle car but with modern refinements. Quite heavy but handled well for a road car. Very sensible running costs (excluding fuel) and completely reliable but again, not so good on the weekend/special car sense of occasion feeling which is what a weekend car really needs!
I was about to jump back into an Aston maybe try a Granturismo a couple of months back. I was looking at cars at around 40k when I spotted for sale the Gransport that's now in my profile pic.
Always liked them, and I think I fell in love a bit with this one, so long story short I bought it! I paid much less than half of my Aston budget for this car and comparing the Aston to the Maserati, I would honestly say that the Gransport is 90% as good with the biggest advantages being:
1, More power than the 4.3 Aston, and it feels much quicker and firmer/sportier.
2, F1 gearbox in the Gransport is MUCH better than Astons Sportshift.
3, Nearly the same sense of occasion/ special car feeling. (Aston are really very hard to beat here!)
4, At the moment, Gransports can be picked up at half to two thirds the price of a Vantage.
5, seats, without it feeling like it if that makes any sense!
So after all that, and considering this is after all a Maserati Forum, I think you should take advantage of the current Gransport prices and then make it perfect with all the money saved!
Failing that, I think an 07 08 Aston V8 Vantage 4.3 manual (or 4.7 at a push for budget) would tick all the boxes very well. Really great, rewarding and special cars to own and drive.
As for other maybes that keep catching my eye, how about...
Jaguar F type R
Granturismo 4.7
TVR T350 (make sure you know what's been done to any speed 6 in terms of rebuild history)
Exige V6 (May be a little raw still)
Audi R8
Would love to see a pic of your Chimaera 500 by the way!