Hi Helvetica,
I use a 3 jaw chuck on my ML8 and I find it very useful. It's not great for holding wood because the jaws tend to crush the wood fibres and it's really easy to get the wood to slip out of the jaws. However I find it great for holding other things, such as drill bits (as big as you like - not restricted to 1/2" as in Jacobs type chucks), also home made pin chucks and screw chucks, in fact just about anything round (or hexagonal). So personally I would hang on to it. Bits for graduates are not cheap s/h and not so plentiful (I have a graduate so I've found that out) so this chuck may enable you to adapt perhaps other manufacturers' accessories which are more easily available (e.g. record).
If you do decide to sell, have a look at the back - there is probably a backplate bolted on which enables the chuck to fit the graduate. This can be changed to suit other lathes. I don't think the graduate thread is a common one for engineering lathes, so a metalworker looking to buy the chuck probably would not want the backplate. However you could use it as a small faceplate, perhaps for a jam chuck etc.
I bought the Axminster evolution chuck for my graduate bowl lathe, cost me £160 and that's £10 more than I paid for the lathe. Then there's the jaws to buy so not cheap overall. However it is a nice piece of engineering and I'm glad I bought it. I was told the type with serrated keys are not as good because the serrations wear on both chuck key and chuck jaws. Also it's not so easy to tighten them up so firmly. The evolution overcomes these issues.
Regarding the value of your chuck - have a look on fleabay, as always. A lot depends on the amount of wear, because metalworkers will want a high level of accuracy, whereas I'm sure most woodturners can manage with a lot less (no offence intended here !!).
K