REM as REM. Later on in sleep the REM stages are longer but it doesn't mean that it's more vivid. I have had dreams that felt super vivid and super long lasting in the first REM stage and some of them have been more vivid than later REM stage lucid dreams. So to summarize: WBTB DILD makes it easier to attain lucidity, but it doesn't mean it makes them more vivid.
Awareness is what makes a dream vivid.