You're original post confuses me, as you're basically saying "I'm having no issues... should I upgrade to an 8GB Graphics Card?"
If you're having no problems, such-as unplayable performance then the simple answer is no.
Still with this said, while 8GB VRAM is becoming "Common"., there are very few games that actually benefit from > 4GB VRAM (as this is the most common configuration, thus is what Developers, such-as myself will target).
On top of this keep in mind that as Game Engines switch from Classic API (DirectX 11, OpenGL or Metal) to Modern API (DirectX 12, Vulkan or Metal 2)., we're capable of manually handling resources...
This is a double-edged sword, given most Developers will initially struggle likely opting for Middleware Graphic Memory Management Solutions (such-as what AMD have on their Open Source, GPU Open Platform) resulting in similar VRAM usage., however this is only true in regards to PC Exclusive Developers; as Historically Exclusively Console Developers (such-as myself) have had very similar Resource Management throughout the tenure of 3D on Consoles.
You're already beginning to see this, but it'll become more common for the "Console" version to not actually be developed initially and separately from the PC version(s)., meaning not only will you have Developers who better understand their Engines (as opposed to 3rd Party Port Teams) but have substantially greater experience with Close-to-Metal / Low-Level Optimisation.
When it comes to Resource Management (VRAM)., the difference between a DirectX 11 Approach to a DirectX 12 Approach, can often mean up to 50% Lower Memory Usage (Frame-for-Frame) as well as considerably lower Data Bandwidth Usage.
This means that 4GB VRAM will actually remain more than viable over the next few years... and this will actually extend, at least on AMD with the advent of High-Bandwidth Cache (i.e. ESRAM Buffer, akin to what the Xbox 360 / One has) that separates the Frame Buffers (which at UHD Resolutions, with Anti-Aliasing, Anisotropic Filtering, Temporal Buffers can be quite Memory Intensive); the same goes for NVIDIA who typically adds this as a Segment of their Total VRAM, hence why they have "Odd" Memory Totals.
Games like Forza Horizon 4 are excellent examples., as said Game if it was in DirectX 11, would *REQUIRE* a Minimum of 6-8GB VRAM for the Ultra Settings; but because it's using a quite well optimised DirectX 12 Engine; instead peaks at 3.6GB VRAM Usage.
Things like Real-Time Raytracing (although I'd argue aren't really "Ready" for Consumer / Gaming, at least not on the scale that Gamers would be impressed by) are actually even more Memory Efficient... which is likely why the RTX 2080Ti only had 8GB instead of the 11GB that the GTX 1080Ti has., as you can guarantee that NVIDIA are utilising it for Driver Optimisation / Acceleration in the background even in non-RTX Games.
Which makes sense, a Hardware Ray Engine isn't exactly "Exclusive" to a Rendering Output approach; but is actually a commonly used for most 3D Mathematics "Grunt Work" … so having Cores that aren't tying that to specifically handling Polygon Raster, Shader ALU Operations, etc. could help, just as it could be used to substantially improve Physics and AI Pathfinding.
It's honestly an exciting technology from a Developer Standpoint., given the freedom it provides; but that's just in regards to backend elements that the Gamer is never going to see or notice... how NVIDIA have implemented it and are currently marketing it to Consumer; well that's just weird., and frankly is likely a stop-gap until they develop an actual "Next Generation" Architecture; which they're falling behind AMD in that regard right now, due to the success of their previous Architecture Base.
Personally, I'd recommend waiting until Q2-Q3 2019 … while I don't believe, or should I say I hope AMD aren't planning to confuse consumers even more by again trying to echo their competition (seriously AMD... keep with the RX Vega [CU] or RX Navi [CU] naming convention; it helps you stand out more, make generations much more recognisable and provide you with freedom to release as few or many SKU as you wish to, without it needing to be shoe-horned into a pre-established Tiered Naming Schema)., the one thing that it seems to echo from my Speculation is the Performance and Price Points.
In essence you'll be able to get effectively RX Vega 56 Performance., as quite literally a direct replacement for the current RX 580.
That's exceptionally great value for Money and Performance.
On top of this the Ryzen 3rd Gen (6 Core / 12 Thread, so Ryzen 5 1600 CPU Performance) with Graphics (20CU, so GTX 1050Ti Performance) is set to essentially offer PS4 Performance at the $140 - 160 Price Point without the need for a Discreet GPU... it wouldn't be a "Massive" performance uplift., maybe like +50-60% over what you currently have; but still one that won't break the bank.
So I'd argue it's worth waiting.
The important thing is, Microsoft stops support for Windows7 in 2020.