We have been facing same dilemma, although have had same tenants for going on 5 years. This past year they were having some marriage problems and husband took over responsibility for paying rent….he is ALWAYS late (only by a few days and it is consistent, he and my husband text back and forth over it, so we plan for it now). Therefore, he ends up sending rent with $100 late fee and we have not raised the rent.
I really think that having good long term tenants has made us lazy. I know we could get a few hundred more a month for the place, but we cover all expenses plus and do nothing….to me it is totally worth not raising the rent to keep them as long as we can.