it's very rare that I'm looking to add a player of the same value
in real life, trading is also not looking at same value. "player wise"
Trading in real life, particularly in the NBA now with Free Agency being what it is, trading is usually for financial gain, be it immediate or long term. Its also it minimze risk - eg: trade away a player whom you know you wont be able to afford next season, before he opts out of his 4th year option, or walks to another team via free agency and you were left with nothing.
If trading were made like this in BB, then the intricacies of free agency, contracts expiring etc etc would need to be introduced. too hard.
I think your statement is very valid and pretty much explains why we don't need trading. Think about it - How many times have you seen Team A buy a player from Team B, and then Team B buy a player from Team A
If someone can show me when this has ever actually happened, I will be astounded.