I'd suggest either Megs APC or a citrus based cleaner, this will help to clear up any engine dirt and grime, may need aggitating on the built up areas and then a gentle wash with an open hose. Run the engine for 10 mins with the bonnet shut, a quick wipe down with a mf cloth for any puddles left and then use an exterior trim dressing on hoses, leads etc.
Had some experience with that, and while yes it shifts the ugly stuff, the hoses discolor (all the white marks on my old volvo that were for people to cut the hoses down based on engine size had gone brown) and the degreaser didn't shift it - the WD did a great job of them though, but you must treat them afterwards!