What do you mean by max strength?
Are you referring to the highest it can when fully researched, which is usually 20 or 21 depending on the machine and what gbv.MaxObjectStrength is in the level file.
Or where research is at the moment in terms of is it worth upgrading?
If it is the last one, I would say yes, but it might look better on the machine menu. That way you could click on a machine and scroll through all your machines to see if any are worth replacing. Or better still it could be on the menu that pops up when you click on the replace button. It tells you the amount at the moment, perhaps alter that text to something like " Are you sure you want to replace the cardio for $1000, its strength is now 15?"