This is a question we think about every year. This is our 13th yr in business, and like you, we have a lot of long time customers, 7, 8, 9 and even 10 year customers. And I've read plenty of threads where people say, "you must raise prices every year."
Well the way I look at it, AT SOME POINT, a customer is gonna be maxed out on price increases. A lawn that started at $40, if you have the customer for 10 years, and only raise his price 2 bucks a season, that same lawn is gonna now be 60 bucks. At some point, the customer is gonna balk, and say, "hit the road jack." SOOOOOOOO, we do not raise prices every year on every customer. We raise customers who have been with a couple of years... But on those special long time customers, you have to think outside of the box.
Where else, can you maybe "hide" the increase"? Maybe on a spring or fall cleanup? An aeration. Mulch. Hedge trimming maybe??? It's easier to raise your price on an extra service, then it is on a weekly cutting.
OOPS... I hit preview, then I went back and re-read your post (sorry), i missed the part where you said you haven't raised some since 2003.... Oh ya, for sure, you can get away with a price increase this year. Obviously the customer is gonna expect an increase sometime. And especially if they are happy with your service, I do not see a long time customer quitting over a couple of bucks. I wish we had your "problem". No doubt we would be raising prices after 7 years if those were our customers. Our problem is different, we have raised prices so much, that a lot of clientele seems to be maxed out. Now we need to find creative ways to hide the increase.