Welcome to both Morgan ownership and Talk Morgan. You will not only find TM to be a great resource, but also a really friendly and welcoming place, with non of the usual backbiting that can go on in other forums.
I bought the most recent Plus Four about a year and a half ago, fitted with the 'dynamic' suspension package, which frankly, was set too hard for my aging bones, however I thought I ought to persevere with the factory setting for the summer, but this year I bit the bullet and decided to play around with things a bit.
It is interesting that your dealer thought raising the height by an inch or so would soften the ride? Obviously he knows best as you paid him $550 for the privilege, however, unless it was bottoming out, I cannot see how this would affect the hardness. Either the dampers need softening or the springs need changing. It is obviously easier and cheaper to start by softening the dampers, which I did. It is best to do this a bit at a time and record the amount of change. The dampers are adjusted by turning a ring at the top - anti-clockwise softens the ride.
You will need to remove the road wheel to access the damper, taking suitable precautions, as you do not want a ton of car falling off the jack. I have started by turning the adjusting ring anti-clockwise by one whole turn on each damper so far. This has made a small, but noticeable difference in the ride, I will probably try another turn soon, when I can motivate myself. Once you are happy with the ride and, if you can be bothered, you can then play around with each end separately.
If you want to return the ride height to its' original position, it is a matter of adjusting the threaded spring seat rings, but be warned that you may need to reset the front toe if you change this, and it may be why your bill was quite high, but there are stacks of workshops with 4 wheel alignment lasers who you could approach, do not think the Morgan dealer is the only one who can work on the car.
Have go, you will be surprised by how easy it is and what differences it makes to your car, which will become more 'yours' once you start loving it. Please post back here once you have done it, as it will help other owners who want to do the same thing. (I would also like to know if my advice is any good too).