Re: Beverley & Dianas clothes...
Real World Reason - they wanted to show off Marina Sirtis' figure so put her in costumes that accentuated her assets.
That's the weird thing. Honestly, I think they failed at this. I mean, Marina's "assets" looked bigger in 2002 when she was on the red carpet for Nemesis than they ever were in the series.
"Those who do not move, do not notice their chains."