Never having opened up an SSD this is purely a guess... but I'd say, no, you probably can't
easily increase the storage capacity of the drive. Several things to consider:
- most likely the Flash memory that's installed inside the drive is NOT in any kind of socket. This means that you can't take a regular thumb drive or SDHC (or similar format card) and swap it with a larger one.
- that being the case, then assume for the moment that the drive manufacturer is using some sort of surface mount technology for soldering the Flash chips to the printed circuit board. Specifically, either SOIC (small outline IC), TSOP (thin, small outline package) or BGA (ball grid array) chip packages. This means that in order to increase the capacity of the drive you would have to remove the existing ICs and replace them with higher density versions (e.g., take existing 16Gb chips and install 32Gb ones). I'd say that most NAND flash in those capacities would have at least 48 pins/balls per device and there's going to be 8 to 16 of them inside the drive. Have fun with your soldering iron

.
- further assume that maybe the drive maker has already reserved "extra" space on the printed circuit board for an additional bank of memory to be added, thereby doubling the capacity. You still have the problem of sourcing those individual SOIC/TSOP/BGA components and soldering them to the board. To give you an idea of the pin spacing on SOIC and TSOP packages, the "pitch", or distance between adjacent pins is around 20 to 30 mils (0.5mm to 0.8mm). BGA packages have the solder balls underneath where you can't even touch them with a soldering iron (it takes a reflow oven to melt the solder and bond them to the board).
- the controller chip that interfaces the outside world to the drive's memory array may be limited to what size it can control.
There may be other reasons that I can't think of but I'd have to say that unless you are "in the industry" (i.e., can get the required Flash memory components for free) and have access to quite sophisticated surface mount reworking stations, then you'll have to bite the bullet and shell out some $$$$ for a larger drive.
edit: Here's several sites where they have done a teardown of an SSD:
http://www.anandtech.com/cpuchipsets/sh ... i=3607&p=2
http://www.tomshardware.com/reviews/Int ... 012-4.html
http://www.hardwarecanucks.com/forum/ha ... iew-4.html
So, the Anandtech site shows an Intel X-25M drive with space on the board for future expansion. Perhaps other drives will have the same type of option. Find some way to get the Flash devices that's already being used in the drive and hope that the designers didn't leave off any other necessary components (resistors, transistors, capacitors, etc.) to make that bank active.