Since no one has replied so far, I will make an attempt, but I am in no way a DCC expert. As you probably know I am strictly O gauge, but I am very interested in trying DCC someday, which would also most likely be in O gauge. My favorite DCC system is NCE. Again no experience, just from reading about it all, which is about all I have done. Maybe it will give you some more to think about anyway?
I have no idea if any given engine is worth adding DCC, but I think the costs will be less than the equivalent upgrades with TMCC or DCS in O gauge. Some of the DCC decoders seem to be fairly inexpensive compared to the options in O gauge. The selections for DCC control and sound upgrades seem to be very good and there seem to be new and/or upgraded items being introduced fairly regularly. IMO there is a very good selection out there, however why you would pick one for any one specific engine over another I have no idea, other than the obvious like better sound, etc. Some decoders are made for certain engines to directly fit (and replace) where their lighting boards or other items are located now and some are more difficult than others as would be expected.
I do know there is a very good selection of decoders available and the sound decoders seem to have multiple horns, bells and other items built that you can choose from, unlike our O gauge items. I have heard some of these and the sound is very good, The speaker size being the limiting factor in the smaller scales, but even some of those small speakers sound pretty darn good these days. Forgot to add above that some of the engines have a wiring connector built in to them where you can get a decoder that will just plug into it and that is it, you are ready to go. Of course you may have to add the speaker of maybe some other items the engine may not have. I am not yet sure exactly how all this fits together.
The DCC decoders have many more configurable settings than we have in O gauge. I think the O gauge manufacturers have a lot of these built in and pre-programmed. DCC has CV's (configuration variables) that you can set to different values to change many things about the way your engine operates. There are NMRA standards for these, but the decoder manufacturers use different ones for different things so they are not all exactly the same. Some also have many more settings than others. That is the short info, I imagine there are books written about these if you want to go deeper. Anyway, with DCC it seems possible to set almost anything the way you want it if you get the right control and sound decoders.
One reason DCC interests me is all these settings to fiddle with and the selection of decoders seems almost endless. The sounds also seem to be very good from some of the decoders. Some that I have heard were very impressive compared to some of ours in O gauge. Also they seem to be improving at a faster pace than our O gauge items and I think there is a lot more available in other areas as well, like computer control (PC) among others.
Hopefully someone with experience will be along to provide more specific details.
