First off. I have 8 SSDs (two desktops and two laptops. SSDs date back to Intel G1 (3 generations ago). I have yet to have one fail or to lose any data. I love them and would not go back to a Mechanical HDD as the boot drive/program drive.
Need to evaluate the benifit you would get vs the cost.
SSDs provide extremely fast boot times and program load time. Once you are in windows and have loaded your program(s) then unless you are runing a disk intensive program (you did not indicate any) there is little performance benifit.
Trading, if that is stock trading/monitoring SSD/HDD does not matter you should have two, The 2nd one could be a USB HDD. Keep your OS + program disk small (and based on you current size usage a 128 gig (Note true size 90->111 gigs) would be great for SSD and the same size for your "C" drive.
With windows 7, protecting yourself is very easy. Windows 7 added a back up feature that allows you to store an image file of your C drive on the 2nd HDD. Should you lose your C drive you can restore it in about 10->15 min. This Sure beats the HE^&^& out of re-installing and re-loading all the drivers and programs.
In your case, you want reliability. If SSD is for you I'd recommend the samsung 470. This SSD has the least number of complaints, and sure beats the HDD every way to Sunday in terms of performance (keep in mind what I said at the begining.
Me I'd go with the Samsung 470 (alternative is the curcual M4 - Stay away from Intel 320 and OCZ XXXX Sata III drives) and a small 320 -> 500 Gig SATA II HDD. There is no real advantage to a SATA III HDD.