I blind buy things if they look appealing since I have very good filtering in place to spot things I like. I don't mind taking a punt but there are some situations where streaming does affect my purchasing, for example:
1. I didn't think I'd like Fate/Stay night but I bought MVM's DVD set back in the day because it was cheap. Actually, I didn't really like it and wanted to punch the entire cast. But when Fate/Zero popped up for streaming I gave it a go and loved it, so much so that I bought the very expensive 'import' BDs. A massive win for streaming (and a massive loss for my wallet). Without the stream I would have bought a cheap complete collection at best. The series seemed to do quite well for MVM in special edition form too, probably in part due to people who felt like me but didn't have my budget or who wanted to buy locally.
2. I don't usually really love comedy because I'm a humourless old git. But then Gekkan Shoujo Nozaki-kun streamed and I adored it, so I joined in the clamouring that Sentai said was needed in order to justify a special edition. Enough people demanded it and one was announced, so I preordered it instead of going for a cheaper version as I normally might have done without my passionate love of Kashima and Hori. Another win for streaming, and for a company which uses modern technology to interact with its fans in positive ways.
3. I wasn't that interested in Arslan Senki since I watched the old version and wasn't blown away back in the day. Anime Limited sorted out a stream for us directly and now I'm champing at the bit hoping they'll license it for a fancy edition soon.
4. I almost skipped Shirobako entirely because it looked like another one of the neverending 'cutesy girls in a club' shows I can't stand. Thank goodness I watched the first episode on Crunchyroll, as it's a much better show than I thought. Shame it's not getting a special edition, eh? (That was a hint.)
R