The cost differentials will all add up:
1. Longer LOA
means higher dockage - per foot 5/45 = 11%
2. Wider Beam, fewer and more expensive haul out
3. Greater weight - so more power - engines and sails are bigger (eg L500 with 75HP turbocharged Yanmars will cost more to run and maintain than same sized motor
but normally aspirated 54Hp in L450). Fuel consumption
on a boat with almost 50% more horsepower will be bit higher (but unlikely 50% higher, say 20%?) . If same size engines option, then fuel consumption
will still be higher with greater weight, but probably not a very big difference, but you may wish you had more power at times.
more cost for repair and replacement (look at potential rig wire replacement at year 10)
5. Older boat, more gear
failure as end of useful life approaches on various components (eg, Sail drive diaphragms, hoses, electronics
and so on)
6. More bottom paint
7. Re-sale the L450 is a currently produced and very popular model, think down the track in 5 years, you would be selling a 12-13 year old boat vs a 9 year old.
These are the items that come to mind, some of which are mentioned in earlier posts, on the other hand an L500 is a quicker boat, and has a larger but different salon layout, extra size is possibly better in a seaway, the cabin arrangements may suit you better, but then you are buying
a boat to accommodate extra people in the off-chance that they may join you, when then L450 can be configured to handle a couple more in the salon on the very rare occasion it is needed.
My guess would be operating and maintenance would be 10% higher, capital replacement or major overhaul
costs will come earlier in an older boat, so then there is the time value of money
Any way good luck with your search, either boat would be a fantastic cruising platform.