If I go from 4 client meetings per year to 3, how do I explain the reduction in service?

What I used to say to ideal clients who had gotten accustomed to 4-meetings per year (10 yrs ago), is something like this, "with our fully comprehensive financial services, it's important that you commit to 3 meetings per year so we can get the information we need from you, that only you can provide. So 3 meetings is what we need in order to ensure your plan is on-track and your "financial house" is in order. If you would like to meet more times per year, no problem. Feel free to let me know and we'll put a meeting on the calendar right away."

Nobody called to schedule additional meetings unless something special came up (like a company retirement offer, a death in the family, etc)

The key is to get all your ideal clients scheduled for 3 meetings over the next 12 months (one every 4 months) within the next 30 days or so. Once those 3 meetings are on their calendar (going out a year). Clients will be fine with that. Four months flys by quickly for them (and for you).