My opinion on this has started to shift. I'm in my 3rd year of diving and pretty much bought everything within 6 mos. of getting certified. For the first 2 anniversaries of purchase, I got my reg serviced at the LDS. It cost me approx. $80 for each.
I am fanatical about taking care of my gear. For regs that boils down to proper cleaning after use and annual maintenance. I beg, borrow, and pester the dive shop or a neighbor building for a rinse hose when I get off the dive boat. Worst case I use the tub after I get back to the hotel room. When I get home I soak in warm water in the tub, use a mild detergent meant for gear, and rinse thoroughly. During storage and transport I'm also careful how it's treated and avoid having others setup/breakdown my gear for me.
So the reg cost me $400 and a new one would cost about the same. Based on my conversations with experienced divers, reading posts, reading magazines, reading books (yes!! i love to read about diving!) it seems that the advances in regulators have made them reliable devices with increased life expectancy.
Even if with proper care and annual maintenance, the risk of failure of the reg (or any device) will increase with time and use.
So if I keep my reg for 5 years at $80/yr in maintenance, I'll have spent $400 in maintenance. That means I could buy a new one with that investment. If I sell my old one, which is my current plan, then I can invest that money towards the new reg at 4 years and break even as compared to annual maintenance. If something shiny catches my eye in year 3, I can choose to spend the "extra" $80 and have a new one sooner. This is pretty likely as I like gear and gadgets, love diving, and am fortunate to have discretionary funds to spend on leisure purchases.
So now I'm thinking that my dollars are better spent buying a new reg every 3-5 years rather than spending for annual maintenance.
Of course some would point of that with annual maintenance, my risk of failure, say in year 3 , is higher than if I had gotten annual maintenance and so this is a threat to my life. True. But the failure rates of regs that are well maintained don't seem high within 3-5 years. (of course I can't mathematically quantify that) Then combined with the facts that I have a fully redundant second stage and I always dive with buddy are sufficient risk mitigating factors for me to offset that. If it weren't, I'd be diving with a pony and another reg. A first stage failure could be more dangerous and catastrophic but most failures don't occur there given the design. Oh... And I have that dive buddy. If my trust level with my dive buddy is low such as on trip, then I also keep me and my dive buddy near the dive master during the dive.
