Hi, Lisa. It would help to know what strippers you tried and which worked. Remember that with stripper you are trading off speed against safety. There are many strippers that are safer than others to use but much slower working, particularly on poly. Just about any methyl chloride stripper will work on poly but I think that it is unsafe to use without a lot more protection than the average homeowner has or will use.
A stripper should not hurt the tile but might harm the grout. If you have cleaned up after the stripper adequately, you should be able to regrout without problems. Being relatively flat, the tiles should be much easier to strip than mouldings but 500 sq. ft. is still a lot. But then the cost of replacing 500 sq. ft. of flooring will be expensive too.