It’s hard to say really without hearing the material in question as different situations can require different solutions.
Re bass guitar solos, i mixed some tracks for a local, superb fusion guitarist back at the end of last year, one of which had a beautifully performed fretless with a solo part, in that case the writer had allowed for the solo so made space for it arrangement and dynamics wise so it was just a case of using a reverb (uad lex224 in this case) to help push it forward and create a ‘bloom’ to it. i inserted a high pass filter somewhere around 300hz to stop the bottom end and lower mids getting muddy and that was all it needed.
A delay with a wide stereo setting can help vocals pop by pushing the vocal into the sides a bit more as can ‘stereoising’ a vocal, all context sensitive and subjective of course though 
Hope that helps a bit…
@Mattias… that sounds like an awkward session, sounds like someone had some serious insecurities going on and resorted to diversion with a bit of attention seeking thrown in 