Inclusive or Exclusive?

I have been giving some thought recently to which era to model. This has come about because of the rollingstock I currently have specifically the box cars, many of which have walkways along the roof and therefore would not have been as common during the 1970's/80's as what they are on my layouts.
Over the last few years I have wanted the layouts to be realistic in operation, industry mix, motive power and scenery. To a large degree the scenery and industries I have chosen for the various layouts are representative of the areas modelled (having locals from the areas I model say so is a fairly good indication).

But the era I model is becoming a problem for me. In other words, it is becoming a little too exclusive for me. I figure I have a few options:

• Remove rollingstock / motive power that is outside the era I model from my layouts
• Convert those pieces of rollingstock and motive power so they fit the era modelled
• Broaden the era modelled

I feel the broadening the era is by far the easiest, most likely to work and least expensive. So...

From now on, rather than modelling the 1970's / 80's, the era has been broadened to 1960's-1990's. This is much more inclusive of the motive power and rollingstock that I currently own. This means all the rollingstock and locos can stay as they are! It might also mean that I can include some industries that would not have been specifically modelled in the 70's and 80's which interest me (eg, a scrap metal dealer).