I'm not really someone to comment as I have bought and sold many bikes (and currently have 3 Hondas and a Yamaha, none are an ST...) but in the specific instance of the ST1300, I've owned both an 04 and 09 and couldn't tell them apart except the 04 seemed less knock-prone. If you like the way your aged machine runs (and I have boundless confidence in the longevity of the 1300 motor) but wanted some rejuvenation, I'd throw some money at the suspension (e.g. a new shock, fork springs, fork dampers parts, bushings, head bearings) as that is an area where improvements reward you on every ride.