yeah pretty much except energy cost is relatively stable and arguably lowering with the boom of shale gas and solar panels coming from China. The machines also have become orders of magnitude more efficient over time so your conclusions apply until you "upgrade" a machine.
What kind of FPGA/board are you using? Are folks still implementing the SHA256 algorithm in dedicated logic? https://github.com/unixb0y/SystemVerilogSHA256 https://github.com/kramble/FPGA-Litecoin-Miner/tree/master/source https://github.com/progranism/Open-Source-FPGA-Bitcoin-Miner/tree/master/src https://en.bitcoin.it/wiki/Block_hashing_algorithm
Looks like a difficult decision on where to start. Does the OP want to test the water first or jump in? I would stay away from FPGA's and focus on either GPU or ASIC. The GPU is more flexible. The ASIC is more specialized and efficient. There are pro's and con's to both. I would say flexibility is nice for starting out. Also, the resale value of GPU's has held up fairly well. GPU's have other use cases. The ASIC miner is a one trick pony. Once the value drops, it will drop hard. Depending on how much you spend, you could make money faster with the ASIC miner though. The choice is really up to the OP. On the topic of FPGA miners. I noticed a lot of the popular FPGA miners and firmware are all closed source these days. Closed source FPGA is great for people developing the miners but bad for the end users. The users are at mercy of whatever the vendor provides and users can't update or upgrade the miners themselves if development support stops. This is called vendor "lock-in." You lose a lot of the beauty of the FPGA at that point.