A few ideas:
1) Take an honest look at your dog's weight. Is he currently at a good weight (by which I mean normal or slightly below normal), or is he overweight still? Losing 10 lbs is great...unless he needed to lose 20-30! (I don't have an opinion based upon your photo.) If your dog is AT ALL overweight, this is THE most important thing that you can do to help him.
2) Metacam is a great medication, but is relatively expensive (in the liquid form) and in many cases doesn't have a big advantage over other, similar medications. You can also purchase Metacam as the human generic tablet (Meloxicam) relatively inexpensively from a human pharmacy. So, talk to your vet to see if your dog could be safely dosed with the tablets, or if another less expensive NSAID medication would be a possibility. He may have strong reasons for wanting to use Metacam oral liquid, or he may not, but you won't know until you ask.
3) As you mentioned, Adequan is intended to be used as a "loading dose" twice weekly for 4 weeks and then on an "as needed" basis (usually every 3-6 weeks). If you didn't do the loading dose phase, you may not be getting the full benefit from that product. FYI, your vet is giving you a screaming deal on the laser+Adequan treatments.
4) Here is a little tough love for you: Most of the older/arthritic dogs out there are significantly painful, and most owners are in total denial about how bad the situation is, mostly because they are looking for SEVERE symptoms before they think their dog is painful. If your dog is having episodes of being significantly stiff/painful, he is painful enough all of the time to benefit from regular treatment (i.e. daily). The whole business about treating "as needed" or using half doses, or only treating if you see him limping is basically a line of B.S. that all vets dispense, trying to make our client's wallets happy. So, assuming that you can afford to do so, stick with some regular therapy and your dog will be much happier.
5) You didn't mention if (or when) you had performed bloodwork on him. As you said, you want to have him around for a very long time. That being the case, keep close tabs on his overall health with labwork at least yearly and preferably every 6 months, particularly if you are using more frequent pain medications.
6) There are a great number of natural pain medications and various joint supplements that you can try that are safe and helpful (see the recent thread Natural Pain Relief Post-Surgery for some starting ideas:
http://www.dogforums.com/dog-health-questions/259170-natural-pain-relief-post.html). If you haven't already explored some of these, consider doing so.
7) Assuming that it is available in your area, there is a great deal of research to show that acupuncture is beneficial for dogs such as yours. This is very safe and often not terribly expensive.
8) As a more expensive option, if it is available in your area, physical therapy can be very, very helpful in keeping dogs such as yours healthy. This modality is increasingly available and can include swimming therapy, range of motion exercises, etc. Many dogs treated this way improve their pain levels, their muscle tone, and their joint range of motion. Many of the facilities that perform physical therapy also offer acupuncture, laser therapy, ultrasound therapy, TENs treatment, massage, chiropractic therapy, etc. One of the problems with every other option discussed above is that none of them really address some of the underlying problems that come with age and arthritis: loss of muscle tone, loss of flexibility, loss of range of motion, loss of endurance, etc. While relieving pain is great, it isn't everything. Physical therapy, combined with pain control, seeks to improve the functioning of the entire musculoskeletal system in a way that is almost impossible otherwise.
