Certain techs, as well as certain improvements (Arcean nav center in TA, hyperion shipyard, gravity accelerators trade good) give a +1 passive bonus to speed.  In TA, the base speed is raised to 2 as well.  Furthermore, +1 speed only costs 5 points, and the only race that only has 7 points to spend is the DL/DA Torians.  Last I checked, the TA Torians were updated to 8 points, and the Thalans have always been 8 points.  Custom race, which is generally regarded as the best or one of the best options, nets you 15 points.

So which game chapter are you playing, exactly?  And version, for that matter?

Your flagship can auto-survey outside of the range that you can manually send it, although it's not always reliable.  Range is a funny issue, though, and even in a gigantic or immense if you get a foothold on a planet close enough to your opponent, you don't need any range modules.

Additionally, which AIs are you playing against?  Several AIs in TA have an inherent +1 passive bonus to speed-among them the Terrans, Drengin, and Altarians.  Are you noticing the speed discrepancy with all races, or just them?

I've played like 50 games TA all rare setup - there was never any ship from whatever race showing up at my homeplanet.

Nor did any race declare war - as in such a setup some negative factors (e.g. "our close borders") are missing.

When it comes to techs and their using, the computer AI plays to the same rules as you, so apparently if his ships arrive at your planet then he'll have those things researched, pretty easy. Point is, usually first thing to arrive is either Scouts/ Constructors or Colony Ships - but if (as you describe) armed Fighters arrive then it's even late in the game. The AI don't declare war so soon - even in a rare Setup they'll start building Colonizers as if in a colonial rush....

Really don't know what you play there..... but you can actually help yourself very easy:

If you wanna know what kind of Techs the AI has already researched simply contact him diplomatically and take a look at his techs. After the initial phase almost all AI's will go researching weapon tech, and that's actually the phase in which you should try to get an own Military Rank, otherwise they will declare war on you sooner or later.

Buy/Trade for a Scout/Fighter - vessel (with a high number). It lets you discover the AI's homeplanet so you can check constantly what ships he's building/ orbiting.

Hope this helps at least a bit.

BTW range scales fairly well up with galaxy size, in an Immense 2 Basic Support modules are usually enough to reach the next inhabited star-system. As all stock ships will have this it's really not un-imaginable that enemy ships reach you over time.

Deleted, was having a dig at a spammer.