I was a Preve turbo owner (bought new in 2015) for 5 years and just got myself an IS250 last year.
Despite its 15 years old age this year (mine is a 2006 Japan recond unit), I would say it's 100% worth to take the leap of faith.

The smoothness of engine (barely feel any vibration at idle) and power delivery of 2.5L V6 engine, as RPM pulls to higher range, is sensational.
Interior space is more cramped compared to Preve (especially the rear passenger seat, only fits 2 comfortably), but the interior quality and NVH is another level.
Reliability wise, in my 1 year+ of ownership, I have only changed the suspensions (normal wear and tear), starter (around RM500-600), battery (again, normal wear and tear) and that's pretty much it.
Very reliable for a 15 years old, 160,000+ km mileage car.
Regular oil change is around RM400 (semi-synthetic oil). Roadtax is around RM870.

I believe 40-50k can get you an IS250. I got mine (directly deal with owner) for around 40k.
Since Mark X and IS250 is pretty much the same car (engine, platform, etc), if you can find one with good condition, I would say go for it!