I don't consider it treasonous to move to greener pastures. Twenty-four years of service is a long time, and being taken for granted is an unpleasant feeling. You have a tremendous amount of responsibility, and you are not being compensated fairly for your skills and experience, given the job market.
Your employer will have lost a good employee, and he has nobody to blame but himself. Clearly he feels no loyalty to you by compensating you appropriately. (You do realize that the people who sit back and accept the we-can't-afford-to-give-raises excuse are perpetuating their own mistreatment, right??) You may be doing what the employer needs: giving him a kick in the butt and scaring him by costing him a valuable employee, one whose credentials make them attractive to other employers.
If your current employer wants to have an exit interview (probably not), be honest and say that you gave the company a more than fair chance to do right by you, as far as fair compensation/training etc. goes, but you need to be thinking about your own future in terms of pension and such, and the new place made you an offer that you couldn't turn down. Say that you have no hard feelings, understand his economic constraints, and perhaps your leaving will allow him to more fairly compensate the people in similar positions to yours (again, he probably won't).