I would not argue with Yooper any day, so grinding in a blender could certainly be an issue. That being said if you have not considered your water I am going to guess you might not be controlling your fermentation temps properly or using enough yeast.
There are a few key items you need to consider to make decent beer. (Not saying you have to and not saying if yu don't do these you are guaranteed to make bad beer.)
1. Fermentation temp control - If you let your brew ferment at ambient temps in your place (say 70-75 F) you are fermenting too warm. While the yeast may say it can work at that temp it will likely be way better if you keep to the cool end of the range. Investigate ways to control temps. This can make a huge difference and is easily the easiest and cheapest way to improve your brews.
2. Pitch the right amount of yeast - Yes a smack pack CAN ferment a full 5 gallon batch, but the current accepted best practice is that creating a starter off your smack pack or vial will give you a more appropriate amount of yeast and help you produce better beers. You can make these in a growler too, so very little equipment is even needed.
3. Water chemistry can play havoc with flavors - If you are doing extract, you don't need to worry too much about this. However, if your water does not taste good plain, this flavor will come through in your beer too. You can always use store bought RO water or distilled. If you are doing all grain brewing you definitely need to consider your water chemistry. This will definitely have an impact on your beers, but not something you need to fix first honestly.
Grain crush is important but I know many who have been brewing for quite a while who do just fine with the crush from the LHBS. That would not be my first purchase. I still don't need one honestly and am a couple years into the hobby doing BIAB.
Hope this helps.
