It was during my research that I discovered the X9 Owners Club. This bunch are one of the finest web communities I have ever found and answered my idiot questions with great good humour. There are as many members who are coming down from big bikes as there are complete newcomers to biking. It transpired that one of the founder members of the club, now a BMW rider had corresponded with me in the past about the Melvin Hunter seat on my R1100RS. What was more interesting was that his old X9, now with another club member, was for sale. Within a week or so, I had sold the R1100RS on eBay and was the proud owner of an X9.
The X9 is without doubt the best scooter on the planet. It's perfectly good in its 125 guise and as a 500 it can easily match much bigger bikes. Maintenance is expensive as it has short service intervals but the storage capacity is enormous (especially with the Piaggio topbox) , it can hit 110 mph (where the law and conditions permit) and fuel consumption is a creditable 50+ mpg. Handling is better than you'd think for a scooter with small wheels and the engine hanging of the swinging arm (as it were) although ride is not great on poor surfaces (which is most of the UKs roads).
However, like the R1100RS, it can be improved and the X9 owners club forums are the place to learn all the little tips and tricks to improve the bike.
One of my real bugbears is that a high volume manufacturer like Piaggio can't be ar**d to fit a proper mph speedo to their bike. To be fair, it's not just them. I once walked out of a well known dealer in Buckinghamshire mumbling loudly about bl**dy grey imports when I saw their 650 Aprilias had kmh biased speedos. I had accepted this downside with the X9 when a member of the forum came up with the answer.
After opening the template in Paint Shop Pro, I tweaked it slightly to highlight 30, 50 & 70 mph in yellow. Once I had printed the template onto thin white plastic, I simply removed the exisitng overlay and replaced it with my new mph dials. Some models have the printing directly on the instruments and this has to be carefully removed with solvent first. This makes the conversion dsomething of a "do or die" activity but mine had a separate overlay. This also means that it can be returned to kmh biased at some point in the future when its a classic and needs to be completely original. There doesn't seem to be any logic to which ones have overlays and which are printed so if you intend to make this change you would be well advised to check it out first.
The dash lights on the X9 are quite bright so the first version had a gentle brown tinge to it. I made a second one by passing the plastic sheet throught the printer twice and this was much improved. In my opinion the new dash looks just like it was factory fitted and a acknowledge a great deal of thanks are due to "Deepblue" who actually did the real work to create the template.
Click here to read the story of the X9s top speed on the X9 Owners Club Forum
On the whole, the X9 is a well put together machine. However, there is one area where quality can only be described as "pants". 
The exhaust silencer is mild steel and is poorly protected against rust. The later "Evo" models have a stainless steel exhaust, but for the SL owner exhaust maintenance needs to be a regular activity, especially on all weather machines. To do the job properly you will need to remove the silencer. There is a heat shield but as you can see on mine the fixings had long since rusted away. 10 minutes with a wire brush is enough to clean up the loose rust thne any one of a number of suitable heat resistant paints can be applied. I preferred the aerosol approach to brushing but you may find that you can "work in" a better coating of paint with a brush.
Removing and refitting the silencer is not much of a problem but you may need to replace the "sleeve" when refitting. This is a compressible mesh bush which is remarkably expensive for what it is. The Paiggio clamp is not up to much and I found that a car exhaust clamp as recommended by Tony at Thompsons made a good replacement.
The X9 was the first bike I had owned with twin headlights. Current legislation means that such bikes only have one light on when on dipped beam. I lost count of the number of times I had to tell muppets that:"it's supposed to be like that - just in case you think that I'm a car that's a long way away !!!!!!!".
Despite that, I think that one headlight on from a pair looks unbalanced and riding on the (pair of) sidelights didn't provide enough visibility. However there is a solution. Replacing the sidelight bulbs with LEDs from Ultraleds provides a pair of bright white sidelights that are unmissable. Not only are they brighter, LEDs are far less prone to failure. The only downside is that they are quite directional. Take a look at My BMW K75 Page to see how I got really carried away with LEDs.