I'm a software engineer and have been working for my current employer for a pretty long while. During this time I have always been a top performer in the teams I have worked in which was well-recognized by both my direct managers and the senior management of the company. Despite of this my salary has always been significantly lower than the market levels for my experience/skills which was due to the fact that I started at a very low salary (intern level) and never negotiated raises (but I was given few 5-10% ones) until a few months ago when I managed to negotiate about 50% increase. I interviewed at other companies in the past few months and I had an offer for an additional 25-30% salary increase, but turned it down for personal reasons. I am pretty sure that if I talk with my boss I can negotiate this 25% increase at my current company as well, but I have been there for way too long and don't see any perspective for future development, so I will most probably continue searching for another job even if I get an increase.
I was wondering - does it make sense to ask for an increase and continue looking for a new job nevertheless? I am pretty indecisive about switching jobs (i.e. I haven't been interviewing for about 2 months now, although I am absolutely dissatisfied with my current position) so it may take another 1-2-3 months before I start a new job and I won't refuse to take a salary, adequate for my skills during this time, but will it look bad if I get an increase and quit a month later? On the one hand my employer has been paying me ridiculous salaries years on row, but on the other I don't want to burn bridges (basically for the time being my employer loves me, since they made hundreads of thousands due to my naivety)