The big problem with cheap jigsaws is not durability but lack of precision. Way backalong I tried a Bosch and immediately bought one--cost more at the time than all my other portable tools combined but it was worth it. There is no other power tool where the difference between "cheap" and "good" is as apparent as in a jigsaw, but until you've used both you don't realize just how wide that gap is.
Using Bosch blades in your saw if it will take them should help but it still doesn't have the orbital action or precision control of blade movement that the Bosch mechanism (also used in one variation or another by Milwaukee and a couple of other vendors now that the Bosch patents have expired) provides.
If you can't get a smooth cut then you need to smooth it by other means--depending on the intricacy of the cut you can use planes or scrapers or various kinds of sanders.