Hi Daytona - saw this and was a lil disappointed that no one has taken the time to reply.....
I've recently bought my 159 Saloon (Lusso 1.9) having previously owned many 156s inc 1.9 jtd m-jets.
Initial impression is the 159s are much tighter screwed together, but they are a fair chunk bigger, heavier and not as sporting, lot more squishy comfy GT car style. This suits me, but be aware of the difference.
Biggest issues with 159 I have picked up on - power steering - green fluid is what should be in there however numpties at AR put red in there, which doesn't always end well, make sure it is green!
Secondly gearboxes - on the 1.9s they're a weak point, so be sure it has no bearing noises or rumbles / grinds etc coming from it.
other than that you should be fairly set having owned a 156 the usual suspects of inner tyre wear, suspension arms, running temp etc should all carry through. If you owned the 16v JTD 156 previously the engines are near identical.
Places to look is hard - there is no such thing as a bargain on ebay these days sadly, I prefer auto trader but I also hit the pistonheads classified and occasionally gumtree, but I dislike gumtree and seems to have too many "too good to be true" scam looking things on it.
Essentially just keep you eye open and go for one that takes your fancy, that's what I did. I wanted a TI which was late 2009 / 2010 model, however ended up with a 58 plate Lusso purely because it was white with red leather, which really took my fancy.
prices vary massively as range range from 05/06-10 so expect early cars be to down below 5k now and late cars to still be up at 10k.
reasonable for a 2008/2009 car Lusso spec with average miles dependent on condition and history between 6 and 7k?
if you bob me your email address I think I still have the PDF parker's guide I paid for which maybe has some useful info.