If you are buying piston single or twin hours, then in my opinion it will not really help towards an airline job. Why? Because if you haven't flown anything other than a piston aeroplane then (at least here in the UK) you are still considered to be a 'low houred' pilot, even if you have several hundred hours.
This is absolutely true.
How do airline selections happen, from an airline point of view?
1.They look at their needs, say 200 new F/O's to be hired immediately
2.They look at the applications, say 550.
3.Two piles are formed: the smaller one consisting of say 50 pilots with jet/turboprop experience and over 1000 hours TT, the bigger one with all less than 1000 hours applicants, say 500 candidates.
4.Priority is given to the first bunch of
50, routine selection, routine passing,95% pass rate.
5.Moving to the hard part, selection of 150 new F/O's among the 500 newbie applicants: all that's near to 500 hours has made an effort to gain experience through instruction, hour building.
75 candidates out of the 100 who match this profile are selected.Pass rate 75%
6.Still need to select 75 candidates out of straight-out-of-school 400 newbies. Selection based on suitability of candidates.Pass rate 18%
Therefore you are right that piston engine experience is not very valuable compared to jet/turboprop experience but it is good to lift your total experience up and to show the airline you are motivated about aviation, and that you don't smell like the kid coming straight out of school standing next to you.