No. Your understanding of how drives store data is horribly flawed. The notion that you could just upgrade the firmware and suddenly the internals understand how to fit more data is rediculous.
Not every drive has multiple platters. Most laptop drives have just one. Most desktop drives have one, two, or three platters. Understand that on most drives, both sides of the platter are used.
You keep focusing on the idea of clusters and such, but in order to fully understand why there are space limitations, we must inspect how an individual bit gets stored. While computers are digital machines (data is represented as ones and zeros), there isn't any real way to represent a true zero or one in most mediums. This results in defining a certain range of values to represent zero and another range to represent one. When the harddrive writes a zero to a specific position, the write head applies a negative charge (think of it as a -1 charge). When the harddrive writes a one to a specific position, the write head applies a positive charge (this of this as a +1 charge). This method of storing zeros and ones on the harddrive platter is where the space limitations come in. When this charge is applied, it doesn't get applied to an infinately small point of singularity; rather, it has a radiating effect, so the write head modifies a certain radius of the area that it is writing to (Think about dropping a marble in the sand. The marble doesn't only affect the sand directly beneath it; it affects all the surrounding sand). If you put the data too close together, data will start to overwrite itself and you will end up with meaningless data since you can't read back what you previously wrote.
As the technology used in the metals and construction of platters increases and as the technology used in the read/write heads increases, data is able to be reliably written and read from smaller and smaller points that are increasingly close together, thus storing more data per platter. Other technology is also needed. The technology to quickly and accurately position the read/write heads needs to advance so that the heads are positioned correctly for the life of the drive (as a drive ages, the heads tend to drift). Motors also need to be made more and more effiecient so that they don't create too much heat and damage the drive's components.
If you took a platter that was developed ten years ago and used the read/write heads of today, you could never get as much capacity out of that platter as you can from today's platters. If you took the read/write heads used ten years ago and used the platters of today, the read/write heads would never be able to accurately read from and write data to the platters.
There are other limitations to infinite storage than the actual storage device. One of the biggest limitations is addressing. Addressing is how computing systems find data in data storage areas (RAM, drives, etc). If you were able to create a drive of infinite storage today, the most modern operating systems could only be able to use 144 petabytes (144,000,000 gigabytes) of that drive. This may sound like a rediculously large amount of storage that could never be exceeded, but the last addressing scheme could only use drives up to a maximum of 137.4 gigabytes, and at one time, that was considered to be rediculously large. So, in order to use a drive of infinite capacity to its full potential, you would have to have a system with infinite addressing space which would require an infinitely large system bus and an infinitely capable processor.
Oh... By the way, we do store tons of data on our harddrives. While its true that some of the potential of current drives goes wasted, this is necessary to ensure that the drives have as long a life as possible. Consider that the earliest drives stored around a few megabytes of data with platters that had diameters of two feet. In the 1970s, most drives had platters of 8 to 14 inches and stored less than 100 megabytes of data. Harddrive capacities didn't exceed 1 gigabyte until the latter part of the 1990s. The fact that I'm about to buy a 400 gigabyte harddrive is amazing to me considering that I grew up with a computer that had a 120 megabyte harddrive.
