RE: Inverted Circular Saw as a Table Saw?
For me it would be a safety thing;
The table saw comes with such items as a fence, guard, adjustable height (depth of cut) switches and a stable work surface etc.
Even so a Table Saw can be a dangerous tool if not used properly, so I would recommend buying the proper tool the first time and stacking the odds in your favour.
The extra money that you spend will hurt in the short term but I think that the added benefits outweigh the initial cost.
IMHO