To answer your question about styles, I use a style guide that helps new devs/analysts make sure they follow the standard convention. The style guide would contain guidance on:
- Font Size
- Menu Style
- Date/Time format
- Form Standards: Label size/orientation, Required Fields, Tab order,
- Standard Table Layouts: Heading style, Cell style, Cell justification for value type, coloring of rows (watermelon stripe?),
- Common widgets to be used throughout the application
- Alt Text
- Button/Image Guides: Font to use, color, gradients, etc.
- Icons to use
- Hover style/delay
- Usage of Breadcrumbs
- Tree Style
- Use of Popups
- Error Message Styles (Error, Informational, Warning, Custom)
I use the term 'guide', because it's just that: a guide. It's not a requirement, since different situations warrant different solutions. However, any deviations should be discussed with the team, to make sure it's the right approach. Perhaps a new style needs to be added to the guide.
As for the applications ....I have a similar situation.
One of the applications I work has been built for EVERYONE, and now it pleases NO ONE.
Making the system pretty may not make it more functional. And I can't make any changes that adversely impact my advanced users which know where every field is that they need to use.
I'm sure that if you analyzed the data, you would see only 20% of the fields used constantly, and the other 80% of the fields used only in certain cases.