Heres the current lineup (please excuse the mess, didnt have time to tidy up). What should I add for formalish occasions? Something with a dark dial preferably (non-chrono).
I would go for the watchless bracelet bottom left. Otherwise a thin NOMOS would suit the collection, I think.
I think the 2998 on bracelet should work just find....that is killer and will be the best watch at the place
2998 FTW. Pairs fine with a suit at formal occasions! If you want something new or shiny, go rolex BLNR, or new Daytona (if you can find one). Vintage... sky is the limit.
Your inquiry is very vague, leaving the options wide open. I prefer newer and larger watches, for formal occasions I always like the JLC Reverso. The Duo-face comes in 3 sizes and with both a white and "dark face"... http://www.jaeger-lecoultre.com/ca/en/watches/reverso/reverso-classic-large-duoface/3832420.html
You know there will be one guy with a 47 mm panerai with a suit who will look ridculous..... Everybody else will have a Rolex, you want to look like you are knowledgeable and have fine taste... Wear the 2998 on bracelet ... Or on croc strap
If the audience is as you describe with a 2998 they will probably think he was too cheap to buy a new watch instead.
Perhaps an Orient Bambino? Or https://www.amazon.co.uk/Orient-Bambino-Automatic-Applied-ER24004B/dp/B008VBUZDW