A neutral leather conditioner cream would work just fine, for basic maintenance. Regular shoe polish is likely to build up on the surface, so I would avoid it. A lot of people swear by Saphir, but I have had great results with cheap-as-chips Meltonian on shell (I have several pairs of shell shoes though, admittedly, they are all no. 8), so I would expect it to work great on Chromexcel, too. You can also use colored cream: Chromexcel isn't as scratch resistant as shell, of course, so maybe a colored cream is a good idea, if you want them looking "new-ish." Then again, the pull-up is one of the charms of Chromexcel, so, again, I say start with a neutral cream, and see how that does it for you.
It's been four years, so I don't know if you still need it, but I sent a pair of late 60s J&M full-brogue black wingtips to NuShoe (a cheap eBay find, rare in 12EEE), and they came back in wonderful kit. If I didn't have a pair of Church's in black, I'd wear them often (and if I didn't have a pair of Bally Goodyear welted wingtips, in black, I'd wear the Church's). Nothing wrong with the vintage J&Ms, the Church's just fit me better (perfectly compared to very well, and the Bally pair is even better, and are better shoes than either). It wasn't cheap (I did the executive package), but they did an excellent job. Included shoe bags and trees cut for the specific pair of shoes.