A 10 year old H-D is still worth a lot.Hondas are throw away bikes.You can't hardy find parts for older ones,and the V-twin hondas just don't sound right.Like I said it's still a honda.
It's a bike.
It's not an investment.
But let's look at the numbers.
My '06 Suzuki cost $8500. 26K miles so far and it's running strong.
Let's say I keep it for another 3 years, rack up 50k miles, sell it for $3K and then get another for $10K.
In 6 years I've ridden 50K miles, spent a total of $15,500, which is less than buying most brand new '06 Harleys.
I now have a brand new bike with 0 miles and the latest technology.
You've got a 6 year old bike.
Since most Harleys you see in the classifieds only get ridden about 2K miles a year, it's got around 12k miles on it. It might be worth about 2/3 of it's purchase price. If you paid $18k, it's now worth $12k. Still more than mine but your's is a 6 year old bike and the maintenance requirements are going up. It's costing more to keep it on the road.
So the question you need to ask yourself why do you have a bike?
To sell or to ride?
...and yes you can find parts for old Hondas.