You may get better coverage by replacing the WRT54G with a newer wireless N router, but that really depends on the router's location and obstacles between devices.
Wireless repeaters or range extenders are convenient to set up, but reduce data throughput. They're okay for general web surfing, but you may encounter problems when streaming media and experience slower file transfers. I believe a repeater will only work with a single wireless router and not multiple ones simultaneously.
An additional access point is a better solution, but you will need wiring between your existing router and access point. You can run a cat 5 cable or link devices with powerline adapters.
Got 1 Linksys WRT54G Router on the ground floor which uses PTCL DSL Internet and 1 D-Link Wireless N Gigabit Router on the first floor which uses World Call Cable Internet of my house. So yeah we have two internet connections.
Getting weak signals from both of the routers in my room on the far left side of the house and little to no signals in the basement.
So what I want to ask is that should I purchase better routers or should I go with a signal booster of some sorts like an Access Point or a Range Extender?
Also is there such a device which would catch signals from both of these differently configured routers ( different internets, different wireless security keys etc ) and then boost them throughout the house if placed in an area where both the router signals are strong???