Sequential reads are faster than random even on SSD drivers, so it could help but I am not sure how much.
Oh ? Why is that ? SSD still need to address every memory block, don't they ? Or do they have a faster DMA-like mode where you can send the instruction "give me the next 96KB starting at address X ?
SSDs exhibit the same sort of cache locality RAM does. When a region is accessed, a larger chunk is fetched and cached just in case it's needed later.
I'm not sure if a SSD drive have any moving parts and therefor will not benefit from E4rat.
No, it moves the files used in the startup to a closer sector and won't speed up your booting time if you're using SSD discs.
By placing the files together in the memory you may get some extra performance, but it depends on how your SSD is internally organized - you may have some locality effects if the drive pre-fetches more than the block you called for into a cache faster than the flash memory.
With an SSD, the bottleneck for booting is usually hardware detection and initialization, not reading data off the disk. My system takes about 4-5 seconds from the time the bootloader hands off control to the kernel to the time the kernel starts executing the initrd, and another 6-7 seconds to mount the SSD and hard drive, establish the network connection, start system services, and present a login prompt (though starting X and changing resolutions takes another second or two on top of that). I probably can't make that more than 20% faster without getting a faster DHCP server or tweaking various delays and timeouts that exist for good reasons.